Back in the early 2010s, they found a way to spy on HTTPS traffic on the iOS App Store to monitor which apps were getting popular. That's what allowed them to know WhatsApp and Instagram were good acquisition targets.
At this point, I think the race for Zuckerberg is, can Meta survive long enough for the next platform shift (AR or VR) where they will own one of the major platforms and won't need to abide by any reasonable rules before their "internet tentacles" that sustain the Ad Machine are cut off.
My bet is they will make it. Though I don't wish it, they're on track.