How managed updates work
With iOS 11.3 or later, a MDM administrator can delay when new iOS updates appear on supervised devices.
If your organization uses managed updates, you will see the following message in Settings > General > Software Update:
When updates appear
Administrators can delay when new iOS updates appear on supervised devices for up to 90 days. This helps your organization test critical apps and infrastructure with a new update before deploying it.
Administrators can also remotely install an iOS update on your device. If your device uses a passcode, you'll be asked to enter it before a remote update can be installed.