A facebook employee explained me how tracking works. Its not the email address Meta is concerned about. Its the IP, device identifiers and location. Meta doesnt care about the email at all apart from sending you emails for notification. Even with a fake email they exactly know who you are. Let's say you visit CNN.com which has facebook tracker. Facebook has the IP and the device identifiers. Now you login with fake email account on Instagram, facebook knows that's the IP ans the same device hence it "must" be the same person That's how facebook creates shadow profiles.
And people dont share devices?
I have a family pc in the living room. We all use it.
Im not on facebook though.
There's got to be more metadata involved in fingerprinting. The type of content you're looking at. Maybe even deriving some sort of signature from your mouse movements.