There is no need for turning on the iCloud backup on iOS.

In order for the iMessage to have a truly end to end encryption you should turn off the iCloud backup. iCloud Backup, seems to negate the whole e2ee of iMessages and unfortunately there doesn’t seem to be a way to avoid this except turning it off. Only useful thing here (for turning it on) would be for Device Settings / Home screen App organisation. App data hardly needs to be backed up as you can just redownload and login and …

backup icloud ios privacy