This is better to equip the phone with
Reset pushbutton actuated with pin (e.g. unbended paperclip) via small hole on the side (not front and not rear, better) of the phone case.
Or at least pushbutton accessible after rear cover opening. Tap pads instead of pushbutton is last resort.
GNU/Linux is very reliable but also very flexible and upgradeable, what often lead to stuck computer. It will be wise and nice to have the reset pushbutton.
I do not understand modern computers with lack of reset button, hard power off is more stress to components or not desired in many cases.
i.MX8M has relatively complex reset subsystem. Below is i.MX8M specific recipe.
Three pins of i.MX8M is used here.
Reset pushbutton.
For this purpose POR_B (W20) pin must be used with minor additional logic to combine pushbutton output with power management/supervisor ICs.
(Novena schematic is example, but probably better to use debouncing)
Main power on/off pushbutton.
Connected to ONOFF (W21) pin.
Preserve capability to select reset source.
Connect two resistors to TEST_MODE (V7) pin for GND or VCC pulling. (Reference is Novena schematic)
Better, this resistors should be accessible to solder/desolder after rear cover opening only (without other phone elements disassembly)
Note. Novena use i.MX6 (not i.MX8M) but reset subsystems almost identical.
Novena schematic, page 6.
Reference Manual of i.MX8M