This guide will walk you through the prerequisites, the step-by-step methods to enter the mode, and how to navigate it safely.
Lock and unlock the bootloader | Android Open Source Project
This is the standard manual method for most Nokia Android devices. : Completely shut down your using the Power button.
If the adb reboot bootloader command does nothing, your phone may have a different fastboot trigger. In that case, try: adb reboot fastboot (some Android 13+ devices use this).
: Once the screen turns on or you see a small "Fastboot" text or the Android logo, release the buttons.