Hello @crowli13 and welcome to Discussions! I am sorry to hear you can't launch the game after upgrading to Windows 11.
I can confirm that "Assassin's Creed Valhalla" has been tested and is compatible with Windows 11, therefore could you please provide more details to us. What happens when you start the game? Are there any errors or the game does not launch at all. Did you try to launch it from the game library or using a shortcut on your desktop? When you reinstalled the game, have you chosen another partition or was it again an installation path by default?
Please run through this FAQ as it is designed to resolve these issues and let us know if you are able to launch the game now?
Don't hesitate to get back to us if you have additional questions.