Elden Ring is not fully cross-platform. Players on the same console family (e.g., PS4 and PS5, or Xbox One and Xbox Series X/S) can play together via cross-generation play, but there is no cross-play between PlayStation, Xbox, and PC platforms.
It seems like you're referring to Ring Cross Platform — this is not a game. "Ring" usually refers to Ring security devices (like video doorbells), and "cross-platform" generally means being usable across multiple devices (Android, iOS, PC). If you meant something else, feel free to clarify!