https://www.pcgamer.com/rocket-league-players-on-pc-ps4-xbox-and-switch-can-now-play-together-simultaneously/

No download is needed for today's Rocket League update, which brings it into Sony's PlayStation Cross-Play Beta program. That means that, starting today, Rocket League players on PlayStation 4 can play with Switch and Xbox players.

PS4 players could already play with PC players, but the change does affect us. Previously, we could either match with Xbox and Switch players or PlayStation 4 players, but never a mixed-platform group including all of them. With today's change, players on all three consoles and PC can join the same match. As usual, console players will all be designated as "Psynet" players if you're on PC.