How to force quit a program or return to desktop

Hi all. I'm trying out Cachy for the first time and was testing an old game on Steam (Anomaly Warzone Earth). The game went full screen but was stuck in a loading loop where I couldn't Alt+tab or Alt+F4 my way out of. The OS was still responsive and I could open up a terminal but as soon as I did, the game's loading screen would block my view. Is there a way to force minimize or kill a program when it's stuck in full screen? I heard xkill could work but I don't see how to use it when I can't even see the terminal.