Roon 2.65 will not run under Mac OS 10.15.8

They do. This is what the release notes say (or seem to) and indeed it is the only thing that makes sense. And @mjw confirmed it just a few posts up:

There seems to have been yet another miscommunication on this :frowning: @connor

Based upon my experience downloading and installing Roon-pre-2.65.dmg @connor is correct. It only fixes the client side. Of course there could have been an issue with the Core installation that I was unaware of.

After the better part of a morning I was able to recover everything by installing OCLP. I’m double checking all my backups, etc. and will likely migrate the OS to some version of Linux (DietPi?) which I hope will prevent anything like this from happening again.