@mpls, Thanks for posting in Q&A. To remove a personal iOS device from Intune MDM to switch to MAM, the user can simply remove the device from the Intune portal. This will remove the device from MDM management, The next time the device checks in, any company data on it will be removed as Intune also retires a device when deleting it from the admin center. For iOS devices, apps that are pinned to the management profile, all app data and the apps are removed. These apps include apps originally installed from App Store and later managed as company apps unless the app is configured to not be uninstalled on device removal.
You can check what data is removed in the following link:
But the user will still be able to access company apps that are protected with MAM policies. However, the user may need to reinstall company apps if they were previously installed through MDM.
Hope the above information can help.
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