Currently federated identity providers do not provide a separate identity to each site you are authenticated on. At that point any collaborating sites can pull together all the information you give to any one of them. Hell, in most cases your "identity" is your email address, so every site you authenticate with can spam you directly.

"Trust tokens" was built to deal with these issues just for this use case: https://developer.chrome.com/docs/privacy-sandbox/trust-toke...