@cherryandrew, Thanks for posting in Q&A.
From your description, I know your Tenant MDM Authority status was set to Unknown.
Based on my research, here are possible reasons.
1.Your Intune subscription may be expired.
2.Licenses are missing or not assigned to users.
And here are some methods to fix the issue.
1.Ensure there's Microsoft Intune license in your environment and assign to users.
2.you can go to 'Troubleshooting + Support' --> 'Guided scenarios' option from the Intune admin center. When you choose the 'Set up a test device to try out cloud management' option, the MDM Auth selection window automatically appears and allows Intune to be selected.
3.Here is a link you can refer to set MDM Authority to Intune.
https://learn.microsoft.com/en-us/intune/intune-service/fundamentals/mdm-authority-set
Hope the above information can help.
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