It's gotten so bad with Facebook that there's no point in posting all the postings about it, just search on it and you'll get a bunch.
Anyway, what with GDPR, EU citizens now have the right to know what Facebook knows about them.
Facebook is refusing.
Basically, it is saying that it doesn't know what it knows. (Although it really sounds more like "it'd be too expensive for us to find out" is more accurate.)