Next is to login and look at the logs, especially dmesg. Find out how to open a virtual terminal, probably ctrl+alt+f1 (or f2 etc) so you can bypass the display manager to login and poke around. Or try SSH from another system. There’s a couple of ideas, good luck!

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Address already in use is the key - something else has already bound to that address:port combination. Next step is to find out what process is listening on it. Try ss, netstat, lsof to name a few hints.

Give each screen other than the “main” one a relative position - left-of or right-of, I think that should do it.

Try going into the Steam settings and make sure that the appropriate controller is enabled for steam input. I had the same issue recently when switching from an Xbox controller to a Gulikit. Enabling Xbox input in Steam fixed it - even though the new controller is not an Xbox controller, and a real Xbox controller worked fine without enabling it.