SOLVED.
TL;DR The stuff in the trash was actually a trash can from my system backup drive (created by Carbon Copy Cloner). Removing the drive caused the trash to be empty. Will reformat the BU drive.
Full explanation
I have been attempting to solve this problem between projects to no avail. Every couple of weeks I would try something. Even had a remote session with Adobe support.
Yesterday I tried a procedure which was to use Terminal commands to move the “.Trash” folder to a tmp folder and reboot. The first step was to get to the trash directory. So I opened the trash folder in finder, typed “cd” in terminal and then dragged the folder from the finder to the terminal where it populated the rest of the command.
I was then going to move on to step two but something caught my eye. I looked at the path the had been populated. Instead of /Volumes/EditDroid/.Trash it was /Volume/EditDroid_BU/.Trashes. (I think Trash being plural was from a previous attempt to get rid of the folder)
The important thing was that the trash was not located on my system drive but on the backup of my system that was created by Carbon Copy Cloner. My guess is that when I uninstalled a Beta of Premiere Pro something got munged during the backup.
So I ejected the drive and now my trash was empty.
20:20 hindsight, I remember with some of the procedures I tried (starting in Safe Mode etc.) I remember that the trash would empty and then after a restart the folder would come back after a few moments. I surmise that it “came back” after a delay was because the external USB drive hadn’t mounted yet.
I am now backing up that backup to a junk drive, then will reformat and reconnect.
Certainly not a common problem, nor life threatening, but glad to have it solved.
Thanks to all who offered suggestions.