Originally posted by OctoberSky:

You may not be consciously using mods but that is the Unity error from mod loading engines like BepinEx due to Unity incompatibility. May need to examine how your game is launched and see if any other loader is coming into play. This latest load moved to Unity 2020.3.33 (Unity itself is Beta on 2022.5.1).

I have reinstalled on two separate occasions?
I'm not really sure where I would look for any mods, or launchers attempting to use Valheim.
Any ideas?