Within this knowledgebase, you will learn how to enable cross-play for your Valheim server.
Step 1:
Log into the Game Panel (located here), and click onto your Valheim Service
"Make sure the server was stopped".
Step 2:
Once on your Valheim Service, click on “Commandline Manager”
Step 3:
Select "Crossplay" and hit save.
Step 4:
Restart / Start your server.
Step 5:
Provide the join code to your friend using game pass to join your server.
(You can use the "Join Code" for both Steam and Game Pass.)
Note: The join code changes every time the server restarts, so don't forget to provide a new join code!