We have noticed that some games (including native games built for Linux) have problems with detecting resolutions: i.e. they detect the resolution of the overall workspace, rather than that of just the main monitor it is running on. For example, if you have two 1920x1080 monitors, the game might detect that you can run it in a 3840x1080 and scale accordingly. In that case the game will show up on both monitors, with broken scaling and misplaced trigger boxes in menus.
In such cases we can recommend temporarily disabling secondary monitors, while playing the game. You can do this in Screen settings/Display.