A day later, and things are better, no thanks to the guy on the Plex forum.
I got up and tried to get it working before I went to the Archives, but I could not. More frustration like last night. After a few hours at the archives, I returned home and resumed this exercise.
While at the archives, I began to toy with the idea of coming up with a new Plex account, see where that would take me. Trying it at home just hopelessly confused Plex. So, I decided to take it to the next level.
After backing up some things on another drive, I reinstalled Linux Mint, overwriting entirely what was there before.
Several hours later, I have downloaded most of the apps I like. Got Dropbox up and running and synchronized with other computers. And, praise be, got Plex reinstalled and running.
For the last few hours, it has been running and trying to get new metadata for the media content I have. I imagine it will be fetching that information all night.
I should not have had to do what I did today. It was patently ridiculous to do this. But it appears to have worked.
Calling it a night. Emotionally beat.
See you tomorrow.