Thanks for the tips.
Disabled plugins, restarted, created empty folder, restarted - folder doesn’t display.
Disabled tag CSS, restarted - same.
Plugins and app are kept up to date.
What’s interesting, if I create an empty folder and leave it named “untitled”, restart and it is missing in Obsidian - but if I try to create another new folder (which starts as “untitled”), Obsidian complains that the folder already exists. So it sees it in the file system, it’s just not displaying it.
Will keep plugging away at it. I’ll just have to start with an empty vault and start applying small # of changes at a time, restart, add a folder and restart again, and see when it disappears.
Thanks again.