Happy Ending!
OK, I had a nice catch up call with Synthax's Jeff Petersen. He was not familiar with Clean My Mac, but I persisted and told him I would follow up.
Clean My Mac found three files in my Apps folder having to do with my 237 install. I removed them from my HD.
I restarted and reinstalled. The installer asked if it could access an external drive. I said OK.
Install was uneventful.
The Mac still could not see the UC although it recognized the 237.
UC wasn't choosable in Apple Pref Audio list or in Logic Pro Audio prefs list.
I chose the Apple Pref Security and Privacy window in Apple Preferences and logged in so I could make changes.
A window opened that showed five files and said they were blocked from loading.
Each file had a box I could click on to select and approve.
One was RME GmbH. I checked that box and the others because I knew what they were, and then clicked on OK.
I moved back to the Apple Prefs Audio window and the UC was there. I selected it.
I opened Logic Pro Prefs > Audio and found the UC in input and output choices.
Bingo! It looks like everything is working.
Two of the previously unloaded files were for digidesign. I'm curious to see if allowing them to load will make my DIGI 003R usable. It became unusable after I upgraded to Big Sur. I was using it as an interface for Logic Pro and it was working quite well.
This is on a 2017 iMac Pro running OS X 11.6. Logic Pro 10.7.1.
Thanks to all for your patience and knowledge. I hope this post will help others.
Regards,
Ty Ford
More at www.tyford.com
Equipment reviews at http://tyfordaudiovideo.blogspot.com