Fullscreen and dark souls 2 sotfs crashing

Are some games not compatible with fullscreening the game window to my whole phone? I cant get it to work with undertale or dark souls 2 sotfs as well as being unable to move past the title screen in dark souls 2 as it stays black out, unable to fullscreen, and then crashes shortly after

I have a regular iphone 15 update 27.0.1