Verify your game files.
Library
right click on game name for Properties
Local Files
Verify

Do that with game shut down.

If that won't help then delete the entire Valheim folder and reinstall / verify files.
corrupted or mod files will not be removed on an uninstall only files the game recognizes.. this should revert you to a "clean" install. Saves are in a different location so no worries there but it never hurts to back up your save files.

Make sure you don't have any mod managers running.