This game is pretty easy to get working on ultrawide with a few simple steps.

First off Set game display mode to "Windowed Fullscreen" this will make the game work on ultrawide monitors however your FOV will be crazy small, this is because the game compensates for the wider fov.

to fix this go to your this folder where you will find the file "engine.ini"

:\Users\......\AppData\Local\StateOfDecay2\Saved\Config\WindowsNoEditor

open "engine.ini"

add the following lines to the bottom of the list

[/script/engine.localplayer]
AspectRatioAxisConstraint=AspectRatio_MaintainYFOV

save the changes then set the file properties to read only! this will stop the game from changing back.

with all this your game should look like the image below hope this helps!!