First of all, one of your friends needs to be searching for a match wether in ranked or training mode in order for steam to display the “Join Game” option.
If you try to join you’ll get a joining message
And maybe fails to join
What i did (i’m serious) is simply mash the “Join Game” button on steam.
This can take a random number of tries, maybe just a couple of tries or several minutes.
Be patient and try until you make it into a lobby.
A very buggy one, as you may have already noticed.
Now leave the lobby.
And here you can search or create your own lobby.
Now all you have to do is invite your friends and play.
It works almost perfectly.
You can also search for some lobbies, but maybe you won’t be able to find any since there is not a lot of people doing this.