With Remote Play Together, you'll play online multiplayer games
Soon Steam will gain another nice feature – Remote Play Together. Thanks to it, it will be possible to start the game in local multiplayer mode, but still online. The service will be available for those productions where players play on the same or split screen. So we are talking about both cooperations and those titles in which we compete with each other. Remote Play Together beta testing will begin this month, October 21
To clarify: it really is only for shared-screen or split-screen games. The tech is streaming your screen to your friend and capturing their input and sending it back to the game, so you are both playing the same game, looking at the same thing.
– Alden Kroll @ PAX Australia (@aldenkroll) October 10, 2019