iMessage's "end to end encryption" has a key escrow backdoor which sends your endpoint keys to Apple and is maintained for the FBI. It's more like "end-to-end-and-Apple encrypted".
It's "end to end encrypted" but then the device's private iMessage syncing keys ("Messages in iCloud") are included in an iCloud Backup, which is not end-to-end encrypted, backdooring the crypto. This means that Apple can decrypt the iMessages as they transit Apple's servers in realtime, using the device private keys you backed up (without e2e) the previous evening.
Even if you turn off the non-e2e iCloud Backup backdoor, your iMessages will still get compromised because it's on by default and all of the other people you iMessage with haven't turned it off.
https://www.reuters.com/article/us-apple-fbi-icloud-exclusiv...
iCloud Photos isn't end to end encrypted at all. It syncs every photo you take to Apple servers effectively unencrypted. Apple can see all of them, and so can the US government (without a warrant). Turning off iCloud is indeed an effective mitigation for this, which keeps your photos on-device.
