Not a book: Advanced Data Protection for iCloud

Advanced Data Protection for iCloud is an optional setting that provides Apple’s highest level of cloud data security.

It uses end-to-end encryption to protect data categories such as iCloud Backup, Photos, and Notes.

To enable this feature, users must have two-factor authentication, a passcode or password on their devices, and updated software on all devices signed in with their Apple ID. Users are also required to set up at least one account recovery contact or recovery key since Apple cannot recover the data if the user forgets their password or loses access to their account.