I concluded that "check for upgrades" was broken, as suggested elsewhere, and 'revert' even more so, so I reinstalled 1.17.0 from a fresh download, which worked just fine.
I incidentally ran across an issue that made CubeIDE unstartable. I haven't checked it out, but what I think I did was to close the IDE with an .ioc file left open in the editor, and then went and deleted the actual project files including that .ioc. So when I started IDE it tried to restore to the edit window the file that wasn't there, and crashed. As I recall deleting the .metadata file in the active workspace solved it. I think this happened with both 1.15 and 1.17.
The original issue with GFX01M2 was the software being incompatible with the $AZ2 version of the PCB compounded by the fact that I plugged it in the wrong way around. With the help from this forum elsewhere, that is now working.