I’m starting to suspect there is a bug in GNOME Shell where the overview occasionally gets “stuck”. No key press or widget click will exit the overview mode. I have to log out and log back in. Launching new windows still works, but the window immediately gets arranged into the overview.
I first noticed this behavior when I tried out the Pop!_OS 21.04 beta, and dismissed it as a bug in the beta. But now I’ve seen it twice in Ubuntu 21.04 proper. Has anyone else noticed this behavior?