Thanks for looking. Indeed I have Firejail installed. I also found a thread right here suggesting a fix.
it works, deleting the org.kde.spectacle desktop file in ~/.local/share/applications brings Spectacle back to life!
However, I also have Ksnip installed, which is still not working, and there is no desktop file for ksnip in that folder. > Discovered an open Ksnip bug Enabling “Force Generic Wayland screenshot” in settings under “Image Grabber” lets me use Ksnip to take a full screenshot, but not selected rectangle.
So, one symptom, two different reasons.