Can't log in, "Logging in to the account failed because an error occurred." and can't open apps

I have a 2018 Mac Mini on Big Sur. I ran into the issue above. I found the fix below...

https://discussions.apple.com/thread/4328284

It worked. I was able to login with my new admin account and verified my old account was still an admin. I was able to log in with my old account once. However, I couldn't open much. When I clicked on most docked apps, they just bounced. Logic worked, FinalCut works, but safari, chrome, pages, numbers, keynote...almost nothing else worked. I rebooted and now can't get into my old account. The new one I just created still works.

I've seen suggestions that it could be my data drive dying. I have my users data on an external drive. All the apps work with my new account, just not my old one. I don't have a backup. I presume if I make one now the issue will be part of the backup.

What are my options? I can save my data and I could reinstall my apps, but hoping there is a fix that isn't reinstall the OS. What is keeping my old account from logging in? It looks fine to me.