STARTING UP FROM EXTERNAL DISKS WITH M1

Monterey changes the way to set Secure Boot policy for bootable external disks on M1 Macs. To drop from Full Security, you have to start up from the external disk, shut down, then start up in Recovery mode by holding the Power button. That takes you into the Recovery system on that external disk, where you can change its policy using Startup Security Utility. When started up from the Recovery system on the internal SSD, you can only set policy for that disk, not external disks.