AGAIN answer this very simple question: How can Sony block a game they don't own on a machine they don't own?
Sony is indeed the one not wanting cross-platform, nobody is denying that. But what is blocked on Switch is blocked by Nintendo, what's blocked on Xbox is blocked by Microsoft and what's blocked on Playstation is blocked by Sony end of story.
Unless you are implying that Sony hacked the Switch servers and injected code that makes those accounts not work on the Switch?
Sony can't block you directly from a service they don't own, but they sure can pressure the owners of said service to do so. I'm sure Sony told Epic to not allow certain kinds of cross platform combinations with their console, and Epic can't really disobey them, otherwise they would face legal repercussions.
You know it deserves the GOTY.