thanks to @BrutalBirdie's continued work on the Valheim game server package, we have no put this as unstable for the time being in the library. I have used it myself and it is already quite usable.
The package repo is at https://git.cloudron.io/cloudron/valheim-gameserver-app
The forum section https://forum.cloudron.io/category/128/valheim
The docs will be collected at https://docs.cloudron.io/apps/valheim/