Is Hellraiser: Revival multiplayer?
No. It is a single-player game, played alone from start to finish: no co-op, no online versus mode, and so no crossplay question.

Modes at a glance
| Mode | Supported |
|---|---|
| Single-player story | Yes |
| Co-op | No |
| Online multiplayer | No |
| Crossplay | Not applicable |
Online features, then
On PS5, online features need a PlayStation account, and on Steam there are achievements, cloud saves and Family Sharing. None of that is a way to play together. The PS5 version supports Remote Play, which streams your own game to another screen, still for one player; more on the PS5 page.
If you wanted to play with a friend
The closest thing is watching: Saber’s trailers and developer diaries are on the trailers page, and the free Steam demo lets each of you try the opening on your own before deciding. The game’s focus on one story, told from Aidan’s side, is laid out on the story page.