If you’ve tried DMZ (like the nuclear option ) and it still didn’t work, that rules out firewall/router issues for the most part. Let’s double-check AMP’s side of things.
Hop into AMP’s interface for the Valheim instance and verify what ports AMP is using under the settings. You can search “Ports” in the top-right search box of AMP to find it quicker. Let’s confirm AMP is configured correctly to match those port forwarding rules!