I’m running stock Linux Mint and when I try to set 16:9 aspect ratio on my 32:9 monitor it stretches the resolution on whole monitor. On Windows it works by putting the screen in the middle of the monitor. I was wondering if something like that is possible on Mint.
I dont have a chance to check specifics but if theres no way to do it using the gui you can try the xrandr command. it has lots of options for screen positioning and the like.