Change your monitor resolution to 2560x1440 or similar when you want to play. It's fast and easy fix.
Also send picture of that cut off screen for dev to have something to figure out what went wrong with scaling.
-*fixed, TRY to make 21:9 work in fullscreen
https://workupload.com/file/ZP7WhXMTmZ4
TRY. no promise
throw to \Data\