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.
There are still...I dunno...probably DNS hops, IP, time's of day, browser window size, browser user agent...
And if you access any page with any similar parameters on your phone or another household device on any site with FB tracking, it's over.
It looks like in the last 7 days my phone has cutoff over 150,000 different tracking attempts and that's just catchable ones and on my phone.