Just thought I'd share my experience setting up a Valheim server with this docker app from @ich777(thank you!)
You don't need to worry about Steam authentication for Valheim, the default anonymous user can download and host a server (yay!), so no fuss with Steam users or Steam Guard to worry about.
Deploy the docker as provided, leaving username & password blank.
The Server Name field is important, this is how your name will appear in the public server list in Valheim. (as of this writing there are 7 "Valheim Docker" server names, good luck finding yours! So choose something unique that you and your friends can find.
World Name is the name of your world, this can be anything, if you wish to import a single-player or self-hosted save file in your docker, this name must be set to the same name/spelling as your save game world.
Save the docker/let it install.
You'll want to make sure your firewall or router has UDP ports 2456-2458 forwarded to your Unraid server's IP so the game can work as intended.
In 10-15 minutes typically you should see your server name in the public server list in Valheim, you're done!
* if you wish to import a previous save file, you need to make sure the Docker is Stopped first. Then browse your local computer's profile, typically in "%appdata%\..\LocalLow\IronGate\Valheim\worlds" you will find your save games.
You'll want to take a copy of your world files, database, everything named the same as your world name over to your docker data files, by default with this docker settings should be:
\\<your unraid server IP or name>\appdata\valheim\.config\unity3d\IronGate\Valheim\worlds
Place your save game files in there, and overwrite any existing newly generated world of the same name with your save game.
Start the Docker, wait for it to appear in Valheim, join & play!
I hope this was helpful for someone, took a bit to figure out the exact steps to follow