Pretty much the title, empty project, when pressing PLAY/PAUSE/STEPTHROUGH Buttons, the left mouse button stops registering on anything Inside Unity except native menus and text inputs.
Does not happen on 2021 version.
Makes the editor 100% unusable without restarting it. - EDIT :: It seems if you enter playmode then everything works again, but it will stop when leaving playmode.
Edit: You dont even need to enter play mode, just pressing the pause button does the same thing.