Did you change the video settings to full screen? I don't have experience with my steam deck and this game, but on my main arch setup I had to change to borderless full screen again. Game wouldn't load otherwise. You either have to change or delete the config. Check ProtonDB for the correct config path.
That is a nice UI but still has the same problems as the official app. It doesn't show all the interactions.
According to this post Mammoth.
https://twit.social/@mbwelch/110268426561442301
I haven't tried it though.
Best I can do are the ones who are either playable or verified:
Could you expand on the relay thing? How does one know if a server uses a relay?
What about the user side? If I want to pick an instance that uses a relay, is there a way to know?
Is this an historical thing? I was really confused when I started using KDE.