@E Saygin, Thanks for posting in Q&A. If the primary user is shown as none in Microsoft Intune, it means this is a shared device or the user has been deleted from Microsoft Entra ID before deleting their enrolled device in Microsoft Intune.
If you want to find last logon user, you can check the usersLoggedOn of a device. Here is a link with more details for the reference:
Hope the above information can help.
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