Reddit:
try going to
"[folder where the game is installed]\some_number\UserData\"
there you should have a file "EuSystemSettingsConfigCurrent.xml".
Open it with your preferred text editor.
Change "eResolution="EQR_1920_1080"" to "eResolution="EQR_2560_1080"" or "eResolution="EQR_3440_1440""
Now launch the game and it should be ultrawide. At least this worked for me.
illetve:
Fullscreen in this game is not a real fullscreen and is actually borderless mode, so change it to that
