Apple screwed the pooch on this with the M1. I confirmed with my 2021 16 inch Apple Silicon M1 MacBook Pro that changing the auto-boot variable using the nvram command in terminal will cause the computer to refuse to boot.
https://eclecticlight.co/2021/01/21/system-management-and-nvram-on-m1-macs/
If this happened to you, recovery is easy. Hold the power button during boot for "boot options" -> click "Options", then click "Continue". Choose a user, then click "Utilities" in the top menu, and open a new terminal.
https://eclecticlight.co/2020/11/28/startup-modes-for-m1-macs/
The default value for auto-boot is "true". Setting this value in nvram can be done like this:
~ nvram -x auto-boot=%01
Listing values in nvram can be done like this:
~ nvram -x -p
Note: -x means use HEX to set and show values.