Personally I don't know but I'm interesting in that. I could try decrypt it if someone provide me first few MiB from disk (and in case if using GPT like on internal, first from encrypted partition(s)), plus of course matching EAP.
However, if access to disk is allowed on another PS4 (probably with the same SEN user account), then disk is't encrypted using EAP for sure but by some static key which all PS4s and PS5s sharing.