How to enable ultrawide resolutions:

[ZenTunE]

Can't post a guide without owning the game on steam so putting this here instead.

Config file is in
"%localappdata%\Mega Cat Studios\Five Nights at Freddy's Into the Pit\#your steam ID#\settings.json"

In the settings.json, simply edit the "FNAF/Settings/Graphics/ScreenResolution": "3440x1440" line to a resolution of your choosing.

No need to set the file to "Read only", works as long as you don't touch the resolution setting in game.

Whatever visual issues and immersion loss this presents I don't know. Just starting the game now, in 21:9. If you try this, please add a comment on your resolution any issues you had, if you had any. I will be doing that too but that will be later.