Coincidental with this discussion of recovery after a disaster, I had just such a disaster and was forced into an emergency recovery of Big Sur.

THE PRESENTING ISSUE

The principal symptoms were the keys on the keyboard did not match what was getting to the computer, and an app ran away throwing up a continuing stream of screens requesting a password, which I was unable to give because of the keyboard SNAFU. This persisted through a reboot, a cold boot, reinstalling Big Sur, and a new keyboard. My computer was in a word — unusable 🤯

MY SOLUTION (Related discoveries in footnotes)
  1. Boot from the Recovery Drive
  2. Erase the boot drive*¹
  3. Clean install of macOS 11 (Big Sur)*²
  4. Recover from Time Machine*³ *⁴ *⁵ *⁶ *⁷ *⁸


RESULTS
  • My system was completely restored incuding all app store and other third party applications. 😎
  • Only one app, BOINC, had to be reinstalled. (I expected that)
  • The only loss was my carefully curated Launchpad folders 😢


CONCLUSIONS

Although the entire process took over four hours, recovery was 100% successful and the entire process was completed with zero loss.

At the present state-of-the-art the Recovery drive and an internet connection are essential to disaster recovery in Big Sur and it appears that is Apple's intent just as it is with the iPhone, iPad, Watch, TV, etc. Whether Apple will create a means of creating a bootable clone or not is an open question and I am not sure I would bet the price of a venti iced mocha, no whip at Starbucks they will.

I still have no clue to what triggered my issue in the first place and I am not happy about that. 😡

FOOTNOTES (aka DISCOVERIES)
  1. When erasing the boot drive, Disk Utility offered to erase only the data volume or the entire drive including even the Recovery volume ‼️
  2. An internet connection is mandatory
  3. Although Migration Assistant found every Time Machine data set on every shared drive on my LAN it did not see the CCC clone of the Data volume on an attached drive.
  4. NOTE: Migration Assistant has to be open and running on other Macs before Migration Assistant will see them as recovery data sources.
  5. A new password was requested for each of the user accounts recovered from Time Machine
  6. In Catalina there is a Time Machine option to NOT include system files and applications. that option does NOT exist in Big Sur
  7. Big Sur Time Machine backups are the entire Data Volume minus any specifically excluded folders (essentially the same data as contained in a CCC clone)
  8. During the restart after recovery I needed my Apple ID and Password, as well as the six digit logon code for my iPad

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein