I guess back in 2021 we had to pretend to believe things like that, because Apple hadn’t yet announced ADP and was refusing to admit they planned an encryption rollout. But they’ve gone and rolled ADP out now: we can stop pretending to believe silly things. Obviously ADP was being planned, and obviously the CSAM scanner was intended to work with it. It got dropped due to the public backlash. A relatively short 16 months later ADP rolled out without it. End of story.
If it pleases you to believe that Apple designed a scanning system that just happened to work with encrypted backup, but intended to turn it off for users who enabled encrypted backup… go ahead and believe that. I would just say, in the most polite way, that maybe if the positive case for Apple’s CSAM proposal requires one to believe such unlikely things, perhaps it is not a very strong case at all.
[1] https://www.reuters.com/article/us-apple-fbi-icloud-exclusiv...
> "If Apple’s CSAM scanner was deployed today, it would be scanning those photos in cleartext on your phone before unreadable data was sent up to the cloud."
Or enabling Advanced Data Protection could have disabled the scanner, we don't know. Even if it went the way you said, you could still not use iCloud and have private photos on your device, whereas your phrasing is trying to imply that there would be no option to do that.