I was under the impression that the messaging apps (WA, Messenger) use end-to-end encryption for the conversations, in which case how does Meta have "access to 70% of all human chat conversations in the last 10 years"?

My own understanding has always been that Facebook cares not one jot about the content of the messages; it's the metadata (i.e. the social network and its patterns of interaction) that's valuable. (Of course that may change, now.)