Today I had the same issue on archlinux with kernel 5.9.14 and gnome shell 3.38.2, it happend right after taking an areal screenshot with gnome-screenshot while in fullscreen, after that when I hovered windows bar and the side dock the cursor became the classic cross you see while taking screenshots and left/right clicking didn't give any result. gnome-screenshot was called by a keyboard shortcut.
Today I had the same issue on archlinux with kernel 5.9.14 and gnome shell 3.38.2, it happend right after taking an areal screenshot with gnome-screenshot while in fullscreen, after that when I hovered windows bar and the side dock the cursor became the classic cross you see while taking screenshots and left/right clicking didn't give any result. gnome-screenshot was called by a keyboard shortcut.