https://www.pcgamer.com/sony-is-looking-at-possibilities-for-total-cross-platform-play/

When news emerged that the Nintendo Switch version of Fortnite supports crossplay with PC, it came as quite the surprise to some. Of the three major console platform holders, Nintendo has a reputation for being the most protective. Nonetheless, at the moment it's possible for players on Xbox One, Nintendo Switch and PC to participate in the same Fortnite battle royale matches.

The one notable exception is Sony's PlayStation 4. While it's always been possible for PS4, PC , Mac, iOS and Android players to compete and collaborate, Sony's device has always notably excluded Nintendo and Microsoft devices. In other words, Sony is the last remaining obstacle on the way to total crossplay compatibility in Fortnite, likewise in Rocket League.