From Startup Manager to Internet Recovery on Intel Macs, and how to engage each of those in an M1 Mac. With comprehensive diagrams.
single-user
Diagnostic, Recovery, Safe, Startup Manager, Verbose, reset SMC/NVRAM, firmware restore, Target Disk/Display, Single-User (SUM) in outline.
Single-user mode to run fsck to check and repair your boot disk became tricky with Fusion Drives. With a T2 chip, it’s not practical in its traditional form.
The Eclectic Light Company 