Have you already tried a completely clean install? That should get rid of any corrupted or modified files, old mod residue, etc.

Uninstall the game via Steam, then go to the install directory, default should be:
C:\Program Files (x86)\Steam\steamapps\common

If there is still a Valheim folder, delete it manually (this will not affect your saves, they are stored somewhere else).

Reinstall the game via Steam.