iMac stuck on 100 % progress bar
Apple has a very good triage step that I follow even after doing a very good job like you in trying to eliminate things (or hope for a quick fix)


https://support.apple.com/en-us/HT204267 (always start with the basics)
https://support.apple.com/en-us/HT204156 (Which leads to general OS startup)
https://support.apple.com/en-us/HT207019 (which is the detailed - just updated and boot fails process)


Why not start down that path and this evening make a good last backup so you can proceed where it says erase and start over?


https://support.apple.com/en-us/HT204904 (The erase and start over process)