> Even if you disable backups, whenever you correspond with someone that has backups enabled those messages are still accessible to Apple.

That last bit is not true. From Apple’s security PDF:

> When Messages in iCloud is enabled, iMessage, Business Chat, text (SMS), and MMS messages are removed from the user’s existing iCloud Backup and are instead stored in an end-to-end encrypted CloudKit container for Messages. The user’s iCloud Backup retains a key to that container. If the user later disables iCloud Backup, that container’s key is rolled, the new key is stored only in iCloud Keychain (inaccessible to Apple and any third parties), and new data written to the container can’t be decrypted with the old container key.

https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/app...