Can't quit SU / "Quit" option greyed out

When I try to quit Sketchup, the “Quit” option is greyed out. Why would that happen?

Sketchup 2019
Mac Mini 2018
Mac OS Big Sur

Here’s a screen shot

Seems like an incompatibility between SU 2019 and macOS Big Sur, though a very strange one. Trimble has never updated anything but the latest release to handle OS updates. SU 2021 is supposed to be Big Sur ready (I haven’t tried it myself, as 3DConnextion doesn’t have compatible production drivers for my Space Navigator yet).

2019 does seem to work ok on Big Sur. For any Mac app, the Quit menu will be grayed out if the application has effectively locked up. Right-click on the SketchUp icon in your Dock, and if the bottom option is Force Quit, then it’s locked up, and all you can do is force quit.

The application has not locked up! Everything still works fine, I just can’t use the Quit command.

Then definitely make sure to save before you Force Quit and try an earlier version of SketchUp.

Are you running plugins, especially renderers?

Same thing happens to me. Quit grayed out, but still can open, manipulate, and save files.
SketchUp 2021
MacOS Catalina
Mac Pro (2015 trash can)

I suspect V-ray may be the culprit, but I haven’t found any further info about it.
Force quitting is an option for SKP, but V-Ray does not appear to have a shut down procedure apart from quitting SKP.