File sharing between two Catalinas - Finder cannot connect
Regrettably I have found no solution to this anomaly. 
I was in the fortunate position to be able to erase and re-install Catalina.   

The problem no longer exists for me. I have a “de-crufted “ system.   

I’m always impressed by how OS X / MacOS has been able to upgrade this Mac successfully for about 6 years with very few of these kinds of anomalies encountered generally in upgrades over the last couple of decades and nearly a dozen different Macs.