Thank you for your reply @miguelaeh!
I was using multi-tier. I actually ran out of time and needed to proceed. I really wanted ( eventually) to port to a single server solution anyway, and I also wanted to upgrade... But I had planned to upgrade first, then look at porting. Anyway, since everything was broken, I just went for it.
I deployed a single-server solution, restored the database there, and allowed Moodle to upgrade itself (v3.4 -> v3.7) I needed to nurse that process a lot by removing data tables that threw errors... But I got it through. Then I transferred the image content file hashes.
So it's up now, on a single server on the latest version, and it all appears good so far. But that was an awfully scary ride, and I don't want to do that again. I'll be playing with the Azure backup/restore before I go any further!
Thanks again for taking the time to offer assistance. Much appreciated.