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 don’t know if this is the same situation but I had the windowing system not configured on X11.
You can get this requirements in this page in the additional requirements table row.
I was using Fedora 31 and switching to gnome (x11) worked like a charm. Unity had never been so cool!