After upgrading Macintosh OS the system does not boot

Upgraded Macintosh OS - System does not boot

Summary

After system was self-upgraded to a newer Macintosh OS using Managed Software Center, the Mac no longer boots.  Typically, either the progress bar stops about 1/2 way, or the Mac boots into a recovery mode.

System keeps going into recovery mode. (Intel chipset)

This case is typically resolved by resetting ("zapping") the Mac's PRAM, sort of like a BIOS Reset.

1. Turn off the Mac or choose to Restart.

2. Just before the Mac boot-chimes, press and hold Command (⌘) + Option + R + P similtaneously ("Reset PRAM").  It's often easier to use command and option on opposite sides of the keyboard with your thumbs, and R and P with your index fingers.  The Mac will continue to chime every few seconds while the keys are held down.  We recommend you hear two chimes.

3. Let go of the keys, then hold down Option, and choose Macintosh HD at the boot picker.  If you're a little late holding option the system may just boot normally; this is fine.

System keeps going into recovery mode. (Apple Silicon chipset)

1. Turn off the Mac or choose to Restart.

2. Press and old the Power button til boot options display on the screen.

3. Select Macintosh HD and press Enter.