Apple has allowed Facebook, TikTok etc. to track users across devices AND device resets via the iCloud Keychain API.

When you log into FB on any account on any device, then install FB on a new device, or even after you erase the device, they know it's you even before you log in. Because the info is tied to your Apple iCloud account.

And there's no way for users to see or delete what data other companies have stored and linked to your Apple ID via that API.

It's been like this for at least 5 years and nobody seems to care.