With Rhino running full screen, I opened ‘Select Layer Color’ dialog. Another app then popped up for a response and, after actioning and closing it, the Rhino dialog was not visible but still had focus. Checking Windows Task View, dialog is still open but any attempt to bring it to the foreground results in the main Rhino window repainting over it too quickly to be able to close it. With the main window full screen I cannot slide it away and without focus I cannot take it out of full screen mode, so Rhino is effectively locked up.
Rhino 7.7.21151.13001, 2021-05-31.
Edit: I was able to close the dialog through Windows Task Manager, leaving the main Rhino process running. As I can’t be confident about the internal state I will close Rhino and restart it though.