Simply turning off iCloud Photos will ensure that photos on your iPhone are never scanned. Why are you trying to make this thing about photos stored on-device? Photos in iCloud have always been available to Apple through iCloud backups. If you are concerned about privacy, turn it off.
"And it does so while providing significant privacy benefits over existing techniques since Apple only learns about users’ photos if they have a collection of known CSAM in their iCloud Photos account."
"And it does so while providing significant privacy benefits over existing techniques since Apple only learns about users’ photos if they have a collection of known CSAM in their iCloud Photos account."