diff --git a/.github/workflows/downgraded_release.yaml b/.github/workflows/downgraded_release.yaml
new file mode 100644
index 0000000..d81472c
--- /dev/null
+++ b/.github/workflows/downgraded_release.yaml
@@ -0,0 +1,35 @@
+name: Downgraded Release
+
+on:
+  push:
+    tags:
+      - '*'
+
+jobs:
+  downgrade_release:
+    if: ${{ !endsWith(github.ref_name, '.74') }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: shivammathur/setup-php@v2
+        with:
+          php-version: 8.1
+          coverage: none
+      - uses: ramsey/composer-install@v2
+      # Downgrade /src to PHP 7.4
+      - run: vendor/bin/rector process src --config build/rector-downgrade-php-74.php --ansi
+      # Optional: Fix coding style (falls ECS genutzt wird)
+      # - run: vendor/bin/ecs check src --fix --ansi
+      # Kopiere PHP 7.4 composer.json
+      - run: cp build/composer-php-74.json composer.json
+      # Entferne Dev-Dateien
+      - run: rm -rf build .github tests stubs ecs.php phpstan.neon phpunit.xml
+      # Tagge und pushe downgradeten Code
+      - name: "Tag Downgraded Code"
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add --all
+          git commit -m "release PHP 7.4 downgraded version" || echo "No changes to commit"
+          git tag "${GITHUB_REF#refs/tags/}.74"
+          git push origin "${GITHUB_REF#refs/tags/}.74"
diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 655c5de..35b916a 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -27,16 +27,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-version:
-          # Not including 7.4, as PHPStan is hard to get working there
-          - "8.0"
-          - "8.1"
-          - "8.2"
-          - "8.3"
-          - "8.4"
-        dependencies:
-          - lowest
-          - highest
+        php-version: ["8.1", "8.2", "8.3", "8.4"]
+        dependencies: [lowest, highest]
 
     steps:
       - uses: actions/checkout@v4
@@ -50,7 +42,6 @@ jobs:
       - uses: ramsey/composer-install@v3
         with:
           dependency-versions: "${{ matrix.dependencies }}"
-
       - run: vendor/bin/phpstan analyse --configuration=phpstan.neon
 
   tests:
@@ -61,16 +52,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-version:
-          - "7.4"
-          - "8.0"
-          - "8.1"
-          - "8.2"
-          - "8.3"
-          - "8.4"
-        dependencies:
-          - lowest
-          - highest
+        php-version: ["8.1", "8.2", "8.3", "8.4"]
+        dependencies: [lowest, highest]
 
     steps:
       - uses: actions/checkout@v4
@@ -81,13 +64,9 @@ jobs:
           extensions: mbstring
           php-version: "${{ matrix.php-version }}"
 
-      - if: "! startsWith(matrix.php-version, 8)"
-        run: composer remove --dev --no-update rector/rector mll-lab/graphql-php-scalars spaze/phpstan-disallowed-calls
-
       - uses: ramsey/composer-install@v3
         with:
           dependency-versions: "${{ matrix.dependencies }}"
-
       - run: vendor/bin/phpunit
 
   code-coverage:
@@ -103,8 +82,37 @@ jobs:
           php-version: 8.3
 
       - uses: ramsey/composer-install@v3
-
       - run: vendor/bin/phpunit --coverage-clover=.build/logs/clover.xml
 
       # Not using v4 due to the breaking changes described in https://github.com/codecov/codecov-action/releases/tag/v4.0.0
       - uses: codecov/codecov-action@v3
+
+  downgraded-build-validate:
+    name: "Downgraded Build Validate (PHP 7.4)"
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: "Setup PHP 8.3 (Rector)"
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 8.3
+          coverage: none
+      - uses: ramsey/composer-install@v3
+      - name: "Downgrade src and tests"
+        run: |
+          vendor/bin/rector process src tests --config build/rector-downgrade-php-74.php --ansi
+      - name: "Prepare downgraded composer.json"
+        run: |
+          cp build/composer-php-74.json composer.json
+          rm -f composer.lock
+      - name: "Setup PHP 7.4"
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 7.4
+          coverage: none
+      - name: "Install downgraded dependencies"
+        run: composer install --no-interaction --prefer-dist
+      - name: "Validate downgraded composer.json"
+        run: composer validate --no-check-publish
+      - name: "Run PHPUnit on downgraded src"
+        run: vendor/bin/phpunit
diff --git a/build/composer-php-74.json b/build/composer-php-74.json
new file mode 100644
index 0000000..40bda2d
--- /dev/null
+++ b/build/composer-php-74.json
@@ -0,0 +1,43 @@
+{
+    "name": "mll-lab/php-utils",
+    "description": "Shared PHP utility functions of MLL (downgraded build)",
+    "license": "MIT",
+    "type": "library",
+    "require": {
+        "php": "^7.4",
+        "ext-calendar": "*",
+        "ext-simplexml": "*",
+        "illuminate/support": "^8.73",
+        "mll-lab/str_putcsv": "^1",
+        "nesbot/carbon": "^2.62.1",
+        "ramsey/uuid": "^3 || ^4.2.2",
+        "thecodingmachine/safe": "^1"
+    },
+    "require-dev": {
+      "ergebnis/composer-normalize": "^2.45",
+      "larastan/larastan": "^1",
+      "mll-lab/php-cs-fixer-config": "^5.10",
+      "orchestra/testbench": "^6.47.1",
+      "phpunit/phpunit": "^9.6.22",
+      "rector/rector": "^1.2",
+      "thecodingmachine/phpstan-safe-rule": "^1.2.0"
+    },
+    "autoload": {
+        "psr-4": {
+            "MLL\\Utils\\": "src/"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "MLL\\Utils\\Tests\\": "tests/"
+        }
+    },
+    "config": {
+      "allow-plugins": {
+        "ergebnis/composer-normalize": true,
+        "infection/extension-installer": true,
+        "ocramius/package-versions": true
+      },
+      "sort-packages": true
+    }
+}
diff --git a/build/rector-downgrade-php-74.php b/build/rector-downgrade-php-74.php
new file mode 100644
index 0000000..577a707
--- /dev/null
+++ b/build/rector-downgrade-php-74.php
@@ -0,0 +1,6 @@
+<?php declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+
+return RectorConfig::configure()
+    ->withDowngradeSets(php74: true);
diff --git a/composer.json b/composer.json
index b0d15fb..3faefa5 100644
--- a/composer.json
+++ b/composer.json
@@ -15,7 +15,7 @@
     "source": "https://github.com/mll-lab/php-utils"
   },
   "require": {
-    "php": "^7.4 || ^8",
+    "php": "^8.1",
     "ext-calendar": "*",
     "ext-simplexml": "*",
     "illuminate/support": "^8.73 || ^9 || ^10 || ^11 || ^12",
diff --git a/rector.php b/rector.php
index 89fb93b..b8aaf24 100644
--- a/rector.php
+++ b/rector.php
@@ -9,6 +9,7 @@
         SetList::CODE_QUALITY,
         SetList::TYPE_DECLARATION,
         SetList::RECTOR_PRESET,
+        SetList::PHP_81,
         PHPUnitSetList::PHPUNIT_40,
         PHPUnitSetList::PHPUNIT_50,
         PHPUnitSetList::PHPUNIT_60,
@@ -19,7 +20,6 @@
         PHPUnitSetList::PHPUNIT_110,
         PHPUnitSetList::PHPUNIT_CODE_QUALITY,
     ])
-    ->withPhpSets()
     ->withRules([
         Rector\PHPUnit\CodeQuality\Rector\Class_\PreferPHPUnitSelfCallRector::class,
     ])
diff --git a/src/FluidXPlate/FluidXPlate.php b/src/FluidXPlate/FluidXPlate.php
index 195e007..c484c6d 100644
--- a/src/FluidXPlate/FluidXPlate.php
+++ b/src/FluidXPlate/FluidXPlate.php
@@ -16,7 +16,7 @@ class FluidXPlate
     public string $rackID;
 
     /** @var Microplate<string, CoordinateSystem12x8> */
-    private Microplate $microplate;
+    private readonly Microplate $microplate;
 
     public function __construct(string $rackID)
     {
@@ -51,7 +51,7 @@ public function addToNextFreeWell(string $content, FlowDirection $flowDirection)
     /** @return Collection<string, string|null> */
     public function wells(): Collection
     {
-        return $this->microplate->wells();
+        return $this->microplate->wells(); // @phpstan-ignore return.type (generic not inferred)
     }
 
     /** @return Collection<string, null> */
@@ -63,6 +63,6 @@ public function freeWells(): Collection
     /** @return Collection<string, string> */
     public function filledWells(): Collection
     {
-        return $this->microplate->filledWells();
+        return $this->microplate->filledWells(); // @phpstan-ignore return.type (generic not inferred)
     }
 }
diff --git a/src/IlluminaSampleSheet/V1/ReadsSection.php b/src/IlluminaSampleSheet/V1/ReadsSection.php
index fcde207..9b7f5db 100644
--- a/src/IlluminaSampleSheet/V1/ReadsSection.php
+++ b/src/IlluminaSampleSheet/V1/ReadsSection.php
@@ -6,9 +6,9 @@
 
 class ReadsSection implements Section
 {
-    private int $read1Cycles;
+    private readonly int $read1Cycles;
 
-    private int $read2Cycles;
+    private readonly int $read2Cycles;
 
     public function __construct(int $read1Cycles, int $read2Cycles)
     {
diff --git a/src/IlluminaSampleSheet/V1/SettingsSection.php b/src/IlluminaSampleSheet/V1/SettingsSection.php
index 6fc8b61..ffadb1a 100644
--- a/src/IlluminaSampleSheet/V1/SettingsSection.php
+++ b/src/IlluminaSampleSheet/V1/SettingsSection.php
@@ -6,9 +6,9 @@
 
 class SettingsSection implements Section
 {
-    private ?string $adapter;
+    private readonly ?string $adapter;
 
-    private ?string $adapterRead2;
+    private readonly ?string $adapterRead2;
 
     public function __construct(?string $adapter = null, ?string $adapterRead2 = null)
     {
diff --git a/src/IlluminaSampleSheet/V2/BclConvert/OverrideCycles.php b/src/IlluminaSampleSheet/V2/BclConvert/OverrideCycles.php
index 03715cf..b8d9558 100644
--- a/src/IlluminaSampleSheet/V2/BclConvert/OverrideCycles.php
+++ b/src/IlluminaSampleSheet/V2/BclConvert/OverrideCycles.php
@@ -15,7 +15,7 @@ class OverrideCycles
 
     public ?OverrideCycle $read2;
 
-    private DataSection $dataSection;
+    private readonly DataSection $dataSection;
 
     public function __construct(DataSection $dataSection, string $read1, string $index1, ?string $index2, ?string $read2)
     {
diff --git a/src/Microplate/FullColumnSection.php b/src/Microplate/FullColumnSection.php
index 6a87c26..759dfa6 100644
--- a/src/Microplate/FullColumnSection.php
+++ b/src/Microplate/FullColumnSection.php
@@ -66,8 +66,7 @@ private function growSection(): void
         }
     }
 
-    /** @return false|int */
-    private function nextReservedWell()
+    private function nextReservedWell(): int|false
     {
         $search = $this->sectionItems->search(AbstractMicroplate::EMPTY_WELL);
         assert($search === false || is_int($search)); // @phpstan-ignore-line function.alreadyNarrowedType (not yet supported by PHPStan of older versions)
diff --git a/src/Number.php b/src/Number.php
index 55a74f0..effa6b0 100644
--- a/src/Number.php
+++ b/src/Number.php
@@ -13,10 +13,8 @@ class Number
      * @param float|int $min
      * @param float|int $max
      * @param float|int $current
-     *
-     * @return float|int
      */
-    public static function clamp($min, $max, $current)
+    public static function clamp($min, $max, $current): float|int
     {
         return max($min, min($max, $current));
     }
diff --git a/src/PHPStan/Rules/NoAssignmentInIfRule.php b/src/PHPStan/Rules/NoAssignmentInIfRule.php
index 039d758..78bc452 100644
--- a/src/PHPStan/Rules/NoAssignmentInIfRule.php
+++ b/src/PHPStan/Rules/NoAssignmentInIfRule.php
@@ -19,7 +19,7 @@
  */
 class NoAssignmentInIfRule implements Rule
 {
-    private NodeFinder $nodeFinder;
+    private readonly NodeFinder $nodeFinder;
 
     public function __construct()
     {
diff --git a/src/PHPStan/Rules/ThrowableClassNameRule.php b/src/PHPStan/Rules/ThrowableClassNameRule.php
index 30c211f..87be9ec 100644
--- a/src/PHPStan/Rules/ThrowableClassNameRule.php
+++ b/src/PHPStan/Rules/ThrowableClassNameRule.php
@@ -13,7 +13,7 @@
 /** @implements Rule<Class_> */
 class ThrowableClassNameRule implements Rule
 {
-    private ReflectionProvider $reflectionProvider;
+    private readonly ReflectionProvider $reflectionProvider;
 
     public function __construct(
         ReflectionProvider $reflectionProvider
diff --git a/src/QxManager/FilledRow.php b/src/QxManager/FilledRow.php
index 5ba9b60..9c38a61 100644
--- a/src/QxManager/FilledRow.php
+++ b/src/QxManager/FilledRow.php
@@ -4,37 +4,37 @@
 
 class FilledRow
 {
-    private string $experimentType;
+    private readonly string $experimentType;
 
-    private string $supermixName;
+    private readonly string $supermixName;
 
-    private string $assayType;
+    private readonly string $assayType;
 
-    private string $targetType;
+    private readonly string $targetType;
 
-    private string $plot;
+    private readonly string $plot;
 
-    private string $targetName;
+    private readonly string $targetName;
 
-    private string $signalCh1;
+    private readonly string $signalCh1;
 
-    private string $signalCh2;
+    private readonly string $signalCh2;
 
-    private string $sampleDescription1;
+    private readonly string $sampleDescription1;
 
-    private ?string $sampleDescription2;
+    private readonly ?string $sampleDescription2;
 
-    private ?string $sampleDescription3;
+    private readonly ?string $sampleDescription3;
 
-    private ?string $sampleDescription4;
+    private readonly ?string $sampleDescription4;
 
-    private string $sampleType;
+    private readonly string $sampleType;
 
-    private ?int $referenceCopies;
+    private readonly ?int $referenceCopies;
 
-    private ?string $wellNotes;
+    private readonly ?string $wellNotes;
 
-    private ?string $rdqConversionFactor;
+    private readonly ?string $rdqConversionFactor;
 
     public function __construct(
         string $sampleDescription1,
diff --git a/src/QxManager/FilledWell.php b/src/QxManager/FilledWell.php
index bd4da93..09394f4 100644
--- a/src/QxManager/FilledWell.php
+++ b/src/QxManager/FilledWell.php
@@ -7,9 +7,9 @@
 
 class FilledWell
 {
-    private FilledRow $famRow;
+    private readonly FilledRow $famRow;
 
-    private FilledRow $hexRow;
+    private readonly FilledRow $hexRow;
 
     public function __construct(FilledRow $famRow, FilledRow $hexRow)
     {
diff --git a/src/Tecan/BasicCommands/AspirateAndDispenseParameters.php b/src/Tecan/BasicCommands/AspirateAndDispenseParameters.php
index a918400..d1bcb27 100644
--- a/src/Tecan/BasicCommands/AspirateAndDispenseParameters.php
+++ b/src/Tecan/BasicCommands/AspirateAndDispenseParameters.php
@@ -6,11 +6,11 @@
 
 class AspirateAndDispenseParameters
 {
-    private Rack $rack;
+    private readonly Rack $rack;
 
-    private int $startPosition;
+    private readonly int $startPosition;
 
-    private int $endPosition;
+    private readonly int $endPosition;
 
     public function __construct(Rack $rack, int $startPosition, int $endPosition)
     {
diff --git a/src/Tecan/BasicCommands/Comment.php b/src/Tecan/BasicCommands/Comment.php
index 9d8f3b9..6053d06 100644
--- a/src/Tecan/BasicCommands/Comment.php
+++ b/src/Tecan/BasicCommands/Comment.php
@@ -4,7 +4,7 @@
 
 class Comment extends Command
 {
-    private string $comment;
+    private readonly string $comment;
 
     public function __construct(string $comment)
     {
diff --git a/src/Tecan/BasicCommands/ReagentDistribution.php b/src/Tecan/BasicCommands/ReagentDistribution.php
index 38ff826..4e7f437 100644
--- a/src/Tecan/BasicCommands/ReagentDistribution.php
+++ b/src/Tecan/BasicCommands/ReagentDistribution.php
@@ -7,22 +7,22 @@
 
 class ReagentDistribution extends Command
 {
-    private AspirateAndDispenseParameters $source;
+    private readonly AspirateAndDispenseParameters $source;
 
-    private AspirateAndDispenseParameters $target;
+    private readonly AspirateAndDispenseParameters $target;
 
-    private float $volume;
+    private readonly float $volume;
 
-    private LiquidClass $liquidClass;
+    private readonly LiquidClass $liquidClass;
 
-    private ?int $numberOfDitiReuses;
+    private readonly ?int $numberOfDitiReuses;
 
-    private ?int $numberOfMultiDisp;
+    private readonly ?int $numberOfMultiDisp;
 
-    private ReagentDistributionDirection $direction;
+    private readonly ReagentDistributionDirection $direction;
 
     /** @var array<int>|null */
-    private ?array $excludedTargetWells;
+    private readonly ?array $excludedTargetWells;
 
     /**
      * @param int|null $numberOfDitiReuses optional maximum number of DiTi reuses allowed (default 1 = no DiTi reuse)
diff --git a/src/Tecan/BasicCommands/SetDiTiType.php b/src/Tecan/BasicCommands/SetDiTiType.php
index ca0ccdb..cfa6d02 100644
--- a/src/Tecan/BasicCommands/SetDiTiType.php
+++ b/src/Tecan/BasicCommands/SetDiTiType.php
@@ -9,7 +9,7 @@
  */
 class SetDiTiType extends Command
 {
-    private int $indexOfDiTi;
+    private readonly int $indexOfDiTi;
 
     public function __construct(int $indexOfDiTi)
     {
diff --git a/src/Tecan/CustomCommands/AspirateParameters.php b/src/Tecan/CustomCommands/AspirateParameters.php
index 070b01f..2d54eeb 100644
--- a/src/Tecan/CustomCommands/AspirateParameters.php
+++ b/src/Tecan/CustomCommands/AspirateParameters.php
@@ -7,9 +7,9 @@
 
 class AspirateParameters
 {
-    private Rack $rack;
+    private readonly Rack $rack;
 
-    private int $sourcePosition;
+    private readonly int $sourcePosition;
 
     public function __construct(Rack $rack, int $sourcePosition)
     {
diff --git a/src/Tecan/CustomCommands/MLLReagentDistribution.php b/src/Tecan/CustomCommands/MLLReagentDistribution.php
index 49c2c4b..b6d3b4c 100644
--- a/src/Tecan/CustomCommands/MLLReagentDistribution.php
+++ b/src/Tecan/CustomCommands/MLLReagentDistribution.php
@@ -12,13 +12,13 @@ class MLLReagentDistribution extends Command
     public const NUMBER_OF_DITI_REUSES = 6;
     public const NUMBER_OF_MULTI_DISP = 1;
 
-    private AspirateParameters $source;
+    private readonly AspirateParameters $source;
 
-    private DispenseParameters $target;
+    private readonly DispenseParameters $target;
 
-    private float $volume;
+    private readonly float $volume;
 
-    private LiquidClass $liquidClass;
+    private readonly LiquidClass $liquidClass;
 
     public function __construct(
         AspirateParameters $source,
diff --git a/src/Tecan/CustomCommands/TransferWithAutoWash.php b/src/Tecan/CustomCommands/TransferWithAutoWash.php
index 8b46b4d..515841d 100644
--- a/src/Tecan/CustomCommands/TransferWithAutoWash.php
+++ b/src/Tecan/CustomCommands/TransferWithAutoWash.php
@@ -13,9 +13,9 @@
 
 class TransferWithAutoWash extends Command implements UsesTipMask
 {
-    private Aspirate $aspirate;
+    private readonly Aspirate $aspirate;
 
-    private Dispense $dispense;
+    private readonly Dispense $dispense;
 
     public function __construct(float $volume, LiquidClass $liquidClass, Location $aspirateLocation, Location $dispenseLocation)
     {
diff --git a/src/Tecan/LiquidClass/CustomLiquidClass.php b/src/Tecan/LiquidClass/CustomLiquidClass.php
index 336f17e..47041a8 100644
--- a/src/Tecan/LiquidClass/CustomLiquidClass.php
+++ b/src/Tecan/LiquidClass/CustomLiquidClass.php
@@ -4,7 +4,7 @@
 
 class CustomLiquidClass implements LiquidClass
 {
-    private string $name;
+    private readonly string $name;
 
     public function __construct(string $name)
     {
diff --git a/src/Tecan/Location/BarcodeLocation.php b/src/Tecan/Location/BarcodeLocation.php
index 8d1d87d..6067c3d 100644
--- a/src/Tecan/Location/BarcodeLocation.php
+++ b/src/Tecan/Location/BarcodeLocation.php
@@ -6,9 +6,9 @@
 
 class BarcodeLocation implements Location
 {
-    private string $barcode;
+    private readonly string $barcode;
 
-    private ScannedRack $rack;
+    private readonly ScannedRack $rack;
 
     public function __construct(string $barcode, ScannedRack $rack)
     {
diff --git a/src/Tecan/Location/PositionLocation.php b/src/Tecan/Location/PositionLocation.php
index 25601dc..50fcad8 100644
--- a/src/Tecan/Location/PositionLocation.php
+++ b/src/Tecan/Location/PositionLocation.php
@@ -6,9 +6,9 @@
 
 class PositionLocation implements Location
 {
-    private int $position;
+    private readonly int $position;
 
-    private Rack $rack;
+    private readonly Rack $rack;
 
     public function __construct(int $position, Rack $rack)
     {
diff --git a/src/Tecan/TecanProtocol.php b/src/Tecan/TecanProtocol.php
index 0b5e255..8f65871 100644
--- a/src/Tecan/TecanProtocol.php
+++ b/src/Tecan/TecanProtocol.php
@@ -22,12 +22,12 @@ class TecanProtocol
 
     public const GEMINI_WORKLIST_FILENAME_SUFFIX = '.gwl';
 
-    private TipMask $tipMask;
+    private readonly TipMask $tipMask;
 
-    private string $protocolName;
+    private readonly string $protocolName;
 
     /** @var Collection<int, Command> */
-    private Collection $commands;
+    private readonly Collection $commands;
 
     public ?int $defaultDiTiTypeIndex;