thats not particularly a wine/proton issue
although proton "could" be having an effect on your WM
thats a WM (window manager) issue with your OS
MATE DE (desktop enviornment) uses Marco WM to draw window frames for you
-- i should know, ive been using MATE for 6 years
I didn't have this sort of issue in anything else then proton, but lets see:
https://bugs.launchpad.net/ubuntu-mate/+bug/1907313
For examples:
I play a video in vlc/firefox/chromium and press fullscreen.
Then i get a full screen on that screen, where the window is, like expected.
Same issue here with 5.13, every game will starts in the second screen.. with 5.0-10 i have btw not problems..
Mate 20.04.1
I don't know how to download old proton version, but i tested a older version of a fork: Proton-5.9-GE-8-ST Version.
When the window is on the second screen he tries to make a fullscreen, but it didn't work.
I think because the resolution of the windows (3440 x 1440) is bigger then the resolution on the second screen (2560 x 1440).
When i move the Window back to the primary screen, it makes a full screen on my primary screen.
This is what i want! I want it back...
=> I don't think it's marcos fault.
proton 5.9-ge-8x1 2020-12proton 5.13-2x1 2020-12
Proton 5.13-2
Games: I think all games are effected, i have this in embr and Rocket League.
Ubuntu Mate 20.04.1
If a game starts in Fullscreen, then it opens in Fullscreen on the primary screen. pefect.
But if you use Alt+Enter to switch into window mode for doing something else and then switch back with Alt+Enter to fullscreen it opens on the secondary screen.
If you leave a game in window mode and you start a game, it will start in window mode. If you hit Alt+Enter it will opens on the secondary screen.
I didn't change anything, but there was a time, where i could drag the window to the desired screen, press Alt+Enter and it will be fullscreen on that screen. This didn't works anymore. It opens everytime on the second screen, which is on the left.