Although does not officially support online multiplayer, players have developed several highly effective workarounds to play with friends remotely. Officially, the game is designed strictly for local co-op only. Official Multiplayer Status
There is no official "online" menu or matchmaking within the game itself. Cuphead online
To play "online," players typically use software that simulates a local environment by streaming the host's screen and sending the second player's controller inputs back. How To Play Cuphead Online Multiplayer | Parsec Blog Cuphead online