@Mark Fleury , Based on my test, I have the empty value under the mobiledevicemanagementauthority property as well.
Then I do more research and test, find we can query the information from the Graph explorer:
URL: https://graph.microsoft.com/beta/organization('your tenant id')?select=mobiledevicemanagementauthority
Request method Get
Modify permission: Need to grant "DeviceManagementServiceConfig.Read.All" and "DeviceManagementServiceConfig.ReadWrite.All" permission.
Hope it can help.
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