[obituary_latte]

Thanks for the reply. So am I misunderstanding their data security overview page?[0]

>For additional privacy and security, 14 data categories — including Health and passwords in iCloud Keychain — are end-to-end encrypted. Apple doesn't have the encryption keys for these categories, and we can't help you recover this data if you lose access to your account. The table below includes a list of data categories that are always protected by end-to-end encryption.

The table includes Messages in iCloud with the caveat that the key is stored in iCloud backups if enabled, but the e2e key is still private, no?

[0]https://support.apple.com/en-us/HT202303

[sneak]

iCloud Backups are enabled by default, and the Messages in iCloud key is in the non-e2ee iCloud Backup.

That means the iMessages being synced are encrypted to an endpoint key which is held by both the endpoint and the middle transit service (iCloud/iCloud Backup). That's end-to-middle-and-end encrypted, i.e. not end to end encrypted.

Even if you turn on iCloud Backup e2ee (it's an option now) then your iMessages to everyone who hasn't (99.9%+ of people) aren't e2ee because the other end of the conversation is backing up their endpoint sync key.