@jarweb,Thanks for posting in Q&A.
From your description, I know you want to export a full inventory of devices registered on Intune and include the last logged on user.
Based on my research, usersLoggedOn stores the last logged on user object id of a device. We can see more details in the following link: https://learn.microsoft.com/en-us/graph/api/resources/intune-devices-windowsmanageddevice?view=graph-rest-beta
Here are the devices result when I check in Graph explorer:
Hope it can help.
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