Finder won't "start"

(iMac Retina 4K 21.5 2017 - running Catalina 10.15.4)

Finder is not initializing properly - all I get is the spinning ball. I updated to 10.15.4 a few days ago and everything was fine until yesterday.

1. I've completed PVRAM reset
2. Done recovery mode disk utility First Aid
3. Created new user account - Finder works normally on that account
4. With the assistance of phone support, gone in and deleted caches, pref lists, etc
5. Reinstalled the OS from recovery mode

I'm out of ideas. I am reluctant to restore from a recent back up until I have no other options.