Desktop gets stuck

Description: the existing windows cannot be moved or closed. New windows cannot be created. Or something else is badly wrong with the desktop.

Hitting the Windows key (between Ctrl-Left and Alt-Left) seems to be a cure.

If this is not the helpful, you have to try the following procedures. The first two are harmless, not on Debian-10, in the sense that all applications remain alive and no user input is lost. On Debian-10 you might getted logged-out. The third, reboot, is the ultimate measure.