does not know the original IP address of the user, the Relay IP addresses rotate over time and between sessions, helping to prevent their use as a stable id...

https://www.apple.com/jp/privacy/docs/iCloud_Private_Relay_Overview_Dec2021.PDF

or Touch ID to sign in automatically. Users can sign in to a new app without filling out any forms or sharing any personal information at all. Just a unique...

https://www.apple.com/jp/privacy/docs/Sign_in_with_Apple_White_Paper_Nov_2019.pdf