Is there a way to force a device to boot into bootloader (not fastbootd) from brom or preloader?

[AndroidHQ254]

Power + Volume Down do not trigger botloader mode on this MT6897 TECNO CAMON 40 Premier 5G. Let me know if there are any specific commands or ways to crash preloader or brom directly to bootloader. Thanks

[n-bilinskyi]

I found a way to enter fastboot (not fastbootd) on OnePlus. Need to put 0xC in WDT bootmode register ( 0x1c00b024 in my case ) using write32 command from preloader, then trigger WDT SW RESET, and hold volume down while rebooting. You need to decompile LK and check maybe same (or similar) method there.

[Make-Error]

Can this work with no auth, or do i need a valid DA?