This page is our investigation of cross-play feature in game called Rocket League. We also want to mention that - we always put manual efforts to find the precise, valid, and what is more important official information about different game features without using AI.
Yes, Rocket League supports cross-play between all available platforms. Players on PlayStation 4, PlayStation 5, Xbox One, Xbox Series X|S, Nintendo Switch, and PC (via Epic Games Store) can play together.
Information about cross-play in Rocket League is from the official game blog; you can check it for yourself by following the link.

Worth mentioning that initially, Rocket League didn't have cross-play support, and it was added later, on January 14, 2019.
Games can have different cross-play combinations, for example the game can have cross-play between PC, Playstation 5, Xbox X|S, but not between old generations like: Xbox One, Playstation 4, PC. To avoid any misinterpretations, we group them into so called "cross-play variations".
Any store inside the cross-play variation have a cross-play only with a store in the SAME variation. We also want to notice, that we put into variation not platform, but store + platform. That is required because some games, for example, can have cross-play between a Playstation 5 and Steam, but not Playstation 5 and Epic Games.