So ever since I switched from Debian 10 to Pop!_OS 20.04, every time I do anything with the game window, (click it, use the play button, etc…) Unity stops responding to left mouse clicks. Right and middle clicks still work, but to get left clicks to work at all in the editor, I have to restart Unity. It’s the same on all recent versions of Unity.
I’m also having this same issue on Manjaro with KDE Plasma. Exactly the behaviour you describe. Stops responding to left mouse clicks anywhere in the editor. Using 2022.1.10f1. Didn’t have this issue with 2019 though. Any help would be much appreciated.