Wow, super weird issue! I really don’t have any definitive answer on how to solve this. I mean, if you’ve restarted your computer and the game is closed, then you should have no problem changing resolution through the windows settings.
I guess what you could try is: go into the options and change the fullscreen mode to Borderless. In this mode, the game can’t affect the windows resolution whatsoever (If it was already on borderless, then it couldn’t realistically have been the game’s fault?). Or have you tried simply changing the resolution in the ingame options?
Anyways, this might just be something with your computer and not the game… it’s hard for me to say. Keep me updated with if you’ve fixed it or not :)