Hey!
I play with a stretched resolution (3:4, 1440:1080) and hate the lower amount of pixels, but also don't wanna switch back to 16:9. I then tried to use 1440:1920(which should be the 4:3 equivalent for 1440p displays) and figured it would just not use the pixels my monitor doesn't have. When I went into the Nvidia control panel and tested that resolution, it worked, just made everything smaller, but when I added the resolution and tried to select it, it just would go back the resolution I was previously on. I don't really get why it isn't working. If someone has an explanation or better yet, a solution, It would be awesome to see that.
Information that may be useful:
GPU: 1070ti
Monitor: 1920:1080 @ 75hz
Game: Fortnite (so as long as I know, the config allows resolution change)