This applet controls fan speed via /sys/class/hwmon/hwmon$id/pwm1, where the
id is provided from settings.
It expects the current user to have read/write privileges on the files in the
hwmon folder, and for the device to support pwm1.
Check if the correct device is used by hovering on the applet
(eg hwmon name: amdgpu for AMD GPUs).
hwmon sysfs Reference
Cinnamon JS Reference Manual
Cinnamon JS Source