Close game -> open device manager -> monitors -> find your 3440x1440 monitor -> right click -> disable device -> open game -> settings -> video -> windowed borderless (i think its called) -> change letterbox to fill -> apply
I cant screen share cuz I'm abt to sleep but where the resolution would normally be try click like Custom I think its called, if not idk valorsnt isn't keen on resolutions that aren't 16:9
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