I have a 32:9 screen and I want to play CS2 in middle, 16:9 way. I couldn't do it natively and tried Gamescope.
While Gamescope works as I would like, the mouse is doesn't work properly. As you can see from the video, game is centered but mouse is aligned to right of the screen. The params I'm using are;
Try turning off display scaling in your desktop settings. It did a similar thing for me, where the game would display at 1440 but acted like the mouse was on a 1080 screen.