Time to see how we did!
Make sure that NetMode is Standalone and there are minimum 2 players
Hit Play
Host a session on one of the windows, define a server name, and hit create session
On the other window that is still on the menu, select Join, and join the session that exists
You should both now be in the lobby map
Select characters for each, ready up, and Start Match
Both players are now in the map together, with their dynamically built aesthetics!
Now you know how to modify ACF Ultimate to have your own Lobby system!
Next steps would be to either integrate Lobby menu functions into the ACF menu (or make your own from scratch) following the examples in the widgets. Its pretty straight forward!
Happy traveling!