In short, Warframe does not support crossplay at all, so if you were hoping to play with other players or friends on different platforms, you can't.
You can, however, play the game cross-gen to a certain extent as the game does support cross-gen for some platforms. In this case, both PS4 and PS5 players can play with each other.
This also applies to all of the Xbox versions of the game, whereas Xbox One players can connect to Seres X/S games, vice versa.
But it still is uncertain when the developers will implement a fully functioning crossplay feature. Hopefully, the developers will implement the feature soon or release news of it since they have already done a cross-gen play for PlayStation and the Xbox versions of the game.
So ideally, full crossplay between all platforms would be next on the chopping block for the Warframe developers. But, yet again, the future is uncertain at the moment as the developers since then haven't released any more information on the subject of crossplay.
That being said, you can find Warframe on nearly all platforms such as the Nintendo Switch, Pc, Playstation 4 and 5, Xbox Series X/S, and Xbox One.