Basically, the MDM authority is automatically set to Intune for the newest tenant service release. Please click this link for more details. https://learn.microsoft.com/en-us/mem/intune/fundamentals/mdm-authority-set
If the MDM authority is unknow, please make sure you have purchased the Intune license.
Besides, even you have activated Basic Mobility and Security for Office 365, you still can use Intune, which can coexist with Basic Mobility and Security.