What is supposed to happen is a player from one side picks a card(s) from a deck. Then places hat card in an area only the other player(s) on his side can see. Later when the player wants to reveal it he will place it face up on the board for all to see.
I tried using a privateside window but I can’t seem to get any of it work right.
You can use the Private window like you have done or the Player Hand window.
Make sure you define in the Map component dialog that access/visibility is
restricted to those sides that you define
What I did in my module for private windows is create a private window for each player and give all the windows the same key command to open it. Then restrict each window to a specific player. This creates a common key command for opening a private window but the only window that will open is the window that is restricted to the player who executed the command.