Editing of preferences.txt only on closed PDE, otherwise it gets overridden …
That was the problem, editor has to be closed for preferences changes to persist. Error message is now gone but still no colored rectangle on the Mac; does work on Windows 11. Lots of ‘nouniform’ in the log window so I know it’s looping. I’ll keep working with it; I don’t see any other error messages. Thanks for all your efforts.