I attempted to upgrade Mint again today and again it failed, this time leaving the machine in an unusable state where python3 wasn’t properly installed and python3 is needed for apt so I could not fix it.

     I could have restored from backups but instead opted to try a fresh install of Mint 20.1 (it was on 19.3), unlike Mint 20, this fresh install succeeded and Mate is working.

     I am still in the process of getting other needed software installed and at least a basic configuration in place so Mint may be unavailable this evening and possibly part of tomorrow depending upon how much I complete tonight.