Once upon a time I sent my then boyfriend a nude on Facebook in a private message. An hour later my account got locked, I had to provide an ID card and prove my identity... Mind you, my profile looks normal and active, 80% of my friends where people in my city that I'd met personally, very few of those accounts had like fake names or nick names. My ex swears he did not report it.
After showing my ID, they unlocked my account. I was at work and a picture of my boobs pops up on that screen with Facebook asking me if that's the image I sent 😬 totally automated, except for the ID identification.
My only conclusion is that a system screened my personal conversation between me and my own then boyfriend.
A private message on fb is still visible and scanned by fb. It is only private in the sense that asking your parents to give a nude pic to your boyfriend is private. The public cannot see it but the delivery service definitely can.
Tech companies have learned that it behooves them to collect as much data as they can, even if they don't have a present use for it. And with AI being so data-hungry, it appears to be paying off.