The Steam page for Returnal on PC has confirmed that the game will not support co-op for various modes or allow for Cross-Play with the PS5 version of Housemarque‘s critically acclaimed title.
The Tower of Sisyphus, House sequences and Challenge Mode are not available in Co-op Mode. Cross-play with players on PlayStation®5 consoles is not supported.
While we’re at it, the Steam page also confirms the recommended system specifications for Returnal:
RECOMMENDED: