Update: I created a new instance and the server on that instance was visible to Steam. No idea why it wasn't working on the old (identical) instance but at least it's working for me now.
OS Name/Version: Windows 10 Pro 10.0.19042 Build 19042
Product Name/Version: AMP 2.3.0.6
Problem Description: Valheim server not responding on local or internet IP
Steps to reproduce:
Start instance in AMP
Start server and wait for it to be running
Use the "connect" option in AMP
Steam's "Game Info" pops up but says "Server is not responding."
Actions taken to resolve so far:
port forwarded on router for ports 2456-2458, 5678-5679, 2224
added host to router's DMZ
added Valheim-server to Windows Firewall rules
added port forwarding to Windows Firewall
turned off Windows firewall
used LAN IP:port
used internet domain:port
checked ports are open via Port Listener and canyouseeme.org
checked which ports are being used by valheim_server using TCP View and forwarded all in firewall/router
toggled server public setting on/off/on again
Edit: I was also unable to get the vanilla standalone DS working until I added -public 1 to start_headless_server.bat - see below
Background: This is my first time using AMP, it's on a brand new mini PC with Windows 10 that's running headless on my local network. I'm administering the computer via RDP and AMP via browser on my desktop. I can connect to AMP management in my browser using mydomain.name:8080 and I have an emby server running on the same domain but I can't get a response from the Valheim server.
Edit: Using the default startheadlessserver.bat script, I was unable to get a response from the vanilla DS (running on its own unmanaged by AMP) until I added -public 1 to the startup script. From that point on the server was visible as expected.