Hi Woody,
you need an assigend role https://learn.microsoft.com/en-us/microsoft-365/security/defender/m365d-permissions?view=o365-worldwide
There is no license needed at all for the administrator account just the approbiate directory role with the permissions.
If you want to recive defender notifications in that account you will need to assign a license with a mailbox type for sure.
Hope that did help with your question. Please give it an upvote and accept it as answer if it did resolve everything.