As of writing, "a default lobby name will be chosen instead" means that the lobby will be named after your Steam persona name.
[SourceLocation("Systems\\Networking\\Transports\\SteamLobby\\SteamLobbySocket.cs", 76)]
private void LoadConfig(LobbyConfig config) // SteamLobbySocket.LoadConfig
{
if (!string.IsNullOrEmpty(config.Name))
{
Networking.UpdateServerName(config.Name);
SteamLobby.SetData("name", config.Name);
}
else
{
Networking.UpdateServerName(Sandbox.Utility.Steam.PersonaName ?? "");
SteamLobby.SetData("auto_name", "1");
SteamLobby.SetData("name", Sandbox.Utility.Steam.PersonaName ?? "");
}
}(Irrelevant code has been omitted)