Hey! I don't often add non steam games so im not an expert. However, just first try and follow the advice by the dev which i'm sure you already have but just in case. If that doesn't work try removing it then doing the same that helped me! Hope i could help! :D
If you can't find the advice then here it is.
If you want to delete the saved data, or you accidently change the resolution of the game and can not change it again then go to:
C:\Users\YOURNAME\AppData\Roaming\Godot\app_userdata\That's not my neighbor