i can't see the whole games when i launch it

i wanted to play citizen sleeper, but each time i launch the games there is black bar on each side of my screen that block part of the games and i don't really know how to change that since the option menu in the games does not allow me to switch the resolution of the games. I would appreciate any advice to fix this ( i got a screen shoot to show you what i mean) , others information i'm playing with a steam deck pluged to a screen .