Worse, iPhones immediately start backing up to iCloud when set up for a new user - the only way to keep your network passwords and all manner of other stuff from hitting iCloud servers is to set the phone up with no network connection or even a SIM card installed.
Did I mention there's no longer a SIM slot, so you can't even control that?
And that iPhones by default if they detect a 'weak' wifi network will switch to cellular, so you can't connect the phone to a sandboxed wifi network?
You shouldn't have to put your phone in a faraday cage to keep it from uploading plaintext versions of your private communications and network passwords.
Are these stored encrypted or in the clear? If the latter, please cite your source.
https://support.apple.com/en-us/102651
The default for many categories is that your keys are in iCloud so Apple can recover them for you. With Advanced turned on, the keys are only on your personal devices. A few categories, like the keychain, are always only on your devices.
Specifically, see Note 3: "If you use both iCloud Backup and Messages in iCloud, your backup includes a copy of the Messages in iCloud encryption key to help you recover your data." Under normal protection, Apple has the key to your backups, but with Advanced they don't.
Oh, you meant... oh.
I thought MDM was only for enterprise businesses and schools and universities, but I may very well be mistaken about that.
Yet, Apple tries to create an image that iPhone is a "secure" device, but if you use iCloud, they can give your contact list to government any time they want.
Apple by default doesn't use E2E for cloud backups, and Telegram doesn't use E2E for chats by default. So Telegram has comparable level of security to that of the leaders of the industry.
