What sync metadata reveals, how device backups differ, and what happens if you lose your iCloud Keychain.
Sync metadata is visible to Apple. Like any CloudKit app, the encrypted records still reveal non-content metadata: roughly how many notes you have, when they change, and their approximate size. The contents themselves are encrypted.
iCloud device backups are separate. Your iPhone/iPad backup (and Mac Time Machine or iCloud Drive, if you back up your home folder) contains Antinote's local database, and standard iCloud Backup is not end-to-end encrypted by default — another reason to turn on Advanced Data Protection.
Losing your iCloud Keychain means losing cloud copies. If you reset your iCloud Keychain (for example after losing all trusted devices), the keys protecting your synced notes are gone and the cloud copies cannot be decrypted — by design. Your notes are still safe on any device that has them locally, and Antinote's local Auto-Backup keeps recent copies of your database.
Extensions are separate from sync. If you install extensions that call external services (like AI extensions), the text they send goes to whatever service that extension uses — that is unrelated to iCloud sync and only happens when you run the extension's command.