If on wayland, go to settings>Preferred Video Driver>Wayland and restart. Without that and the environment vars, the game may run in xwayland and your clipboard may not sync between wayland and x11. The game runs fine if that happens but you may not be able to paste blueprint strings which is a bit annoying. Gamescope isn't necessary and I've tested it without it and it works fine without it, but I just generally prefer it on all of my games. Apart from the clipboard issues, game runs perfectly.