My old software won't run on Catalina. I need to downgrade to Mojave.

Thank you! This is what I recall we were supposed to do.

I wonder if too many of us DIY down-graders found ourselves in deep doo-doo, so Apple developed this "bring it to our shop" program to get it done the right way.

In any event, thanks again for your input. I believe it is exactly what I was looking for!

This works if a Time Machine backup has an old MacOS, like Mojave or maybe one of the Lions. My TM backups are all new and have Catalina. Once upon a time it was possible to erase the HD and install the lesser OS. Not so anymore, according to Support. Now if you don't have the right kind of TM backup you must go to an Apple Service Ctr to have them do the "rollback."

Alas! All the Apple Stores in my region are closed. I'm now looking in the Yellow Pages for an independent Apple Servicer.