Originally posted by Flare |UKCS|:

You can move characters to other worlds, but you cant change a world from single to multi, so you can move your sp toon to a server.
Valheim is not a mmo, its limited to 8 - 10 players (unless modded).

What are you talking about? Opening your world to other players takes one click for friends or a click and setting a password for everyone else.