I've solved most of my monitor problems on Wayland by using Gamescope. For example Enlisted (native) will insist on spanning across my 2 1080 monitors, or Helldivers 2 won't boot on fullscreen while showing a white line on borderless. Also most games won't properly grab the cursor.
On any steam game add this as launch options:
gamescope -w 2560 -h 1440 -r 60 -f -e %command%
This will make the game think it's always running in the foreground, and in the resolution/refresh rate you specify.
If you want to add extra commands, like mangohud or gamemoderun, put them before gamescope
Hope this helps ya, GL&HF