The only things end to end encrypted are listed on this page: https://support.apple.com/en-us/HT202303
If you turn on iCloud syncing, basically you're falling back to simple "in transit" and "at rest" encryption.
A lot of iPhone cracks involve just attacking your iCloud account, and then reading all of your messages from backups. This is not possible on Pixel which encrypt your device backups with on-device hardware encryption.