https://partner.steamgames.com/doc/features/multiplayer/matchmaking
It is a bit hard to find other players to play with on TDS without joining Discord. I think you should integrate Steam matching into a sort of "Server Browser" so that you can find others to play with.
Id expect public lobbies to have a sort of "progression lock" where you'd only be able to join lobbies that are up to the amount you progressed to, so a beginning player can't enter a public lobby all the way in Turbulent, for instance (although they would be able to join if its a private instance with a friend)
#Add a public server browser to find lobbies easier
jolly breach
rich wing