Latest dom0 via CLI update rendered machine unusable, appVMs no longer load, cannot log in as user

[tok100c]

How to file a helpful issue

Qubes OS release

R4.2.3

Brief summary

On desktop with Dasharo (coreboot + UEFI)
64gb ram

Tldr; updated dom0 and now appvms do not load and I cannot log in to machine, second occurrence of this in one year.

I updated machine to latest dom0 release. Used command line qubes-dom0-update. The update completed successfully with success message at the end. However it broke my appvms, which would no longer load. Upon restart, I was able to type encryption pass, but I can't type a username or pass. I assume sys-usb won't load. Ultimately, result is a bricked OS. Unable to log in to the machine. Booting other kernel on startup does not fix.

This same issue happened one other time some months back, when I cancelled a dom0 update. Cancelling the updater broke dom0, I was unable to type username/pass, my machine was wiped out and I took the loss and started fresh. Since then, I have always used cli to update dom0.

I have recovered some essential files using another machine. But is there any chance I can recover the system and repair dom0?

Steps to reproduce

Update to latest dom0 in command line. Continue using appVMs as normal. Let update complete and reboot PC.

Expected behavior

Successful update, functioning dom0 and appVMs.

Actual behavior

Ultimately, a bricked install for a competent but non dev user. Broken dom0, unable to start sys and appVMs.
Second occurrence of this happening, first was due to interrupted dom0 update, second time the update completed successfully.

Thank you Qubes team for all your effort. I will be backing up my qubes from now on. Hopeful I can prevent this from happening again. I'm wondering if anyone else has encountered the same issue.