Which feature or technology locks a supervised iPhone until the feature is turned off?

Managed Lost Modeallows MDM administrators to remotely lock a supervised iPhone or iPad. Once activated, the device is fully locked and cannot be used until Lost Mode is disabled by the MDM. Apple Learning specifies that while in Lost Mode, the device displays a custom message and phone number, enabling it to be returned if lost. Importantly, Managed Lost Mode overrides user settings and does not require the user to have enabled Find My. Unlike Activation Lock, which prevents unauthorized reactivation after an erase, Managed Lost Mode is immediate and active without wiping the device. Return to Service is a redeployment tool, and Device Attestation verifies device integrity but does not lock devices. Therefore, the feature that directly locks a supervised iPhone is Managed Lost Mode.