I think I mentioned this a while back but forgot to mention it, whenever you inspect the Wither Storm with a Spyglass it should give you an Advancement like "Is It The End?" or "Is It a Wither...?"

what about "that's no storm" like a reference to the death star?

That's no Storm... It's a Wither Storm!

Will be implemented in the next 1.18./1.19 release