What phone backups preserve and who holds the keys

A backup and a synced library are different records

Apple describes iCloud Backup as periodic snapshots of information that does not already sync to iCloud. Device settings and third-party app data can be included. Photos and messages can be backed up when their separate iCloud sync features are not used; enabling those features moves that material into the corresponding synced service instead of the daily backup. Apple: backup snapshots versus synced data

The iCloud protection setting changes access to backup keys

Apple says Advanced Data Protection makes iCloud Backup end-to-end encrypted for eligible accounts. Apple cannot recover that protected data without the user's recovery methods. Apple: Advanced Data Protection requirements

Encryption does not remove every cloud record

Apple's security overview says some backup metadata remains under standard protection, including device identity, included apps and snapshot dates and sizes. Mail, contacts and calendars also remain outside Advanced Data Protection's end-to-end coverage. Apple: cloud encryption, keys and metadata

Android backup encryption has category limits

Google says Android backups are uploaded to its servers and some data receives additional encryption with the device screen lock. Google Photos media and carrier MMS media are not protected by that screen-lock encryption. Backup contents can include apps, messages, contacts, settings and call history, but not every app can restore all its data. Google: Android backup contents, encryption and dashboard scope

Stopping backups can have different removal effects

Apple says iCloud backups remain available for 180 days after disabling or stopping iCloud Backup. Its explicit backup-deletion control also turns off backup for that device. Apple: app backup choices and backup deletion effects

Google One says turning off device backup deletes that backup while previously backed-up photos and videos remain in Google Photos. It also describes removal after 57 days without device use. These are device-backup rules, not a promise that every Google service record is erased. Google One: device backup removal and photo exceptions

A computer can hold another sensitive copy

Apple says computer backups are not encrypted by default. Encrypted local backups can include saved passwords, website history, Health and call-history information that unencrypted backups omit. The backup password is needed to use the encrypted copy. Neither type is described as including Face ID, Touch ID or device passcode data. Apple: local backup encryption and password requirements

Availability and account eligibility matter

Apple's UK notice says users there who have not enabled Advanced Data Protection cannot newly enable it. The notice says default end-to-end protection for categories such as Keychain and Health remains. A general feature guide should not be read as proof that every account can turn it on. Apple: UK restriction for new Advanced Data Protection users