@Glenn Evans
Thank you for your post!
I ran into the same issue when trying to run (Get-MgUser -userId 'userID').SignInActivity
. Additionally, when it comes to the Get-MgUser Graph PowerShell command, I didn't see the SignInActivity parameter as a supported parameter within the documentation.
If you're trying to get the SignInActivity for a user, you should be able to follow this 3rd party article written by one of our MVPs - Reporting on user’s last logged in date in Office 365. There's also a PowerShell script that leverages the graph.microsoft.com/beta/users REST API, which could be beneficial to resolving your issue.
I hope this helps!
If you have any other questions, please let me know.
Thank you for your time and patience throughout this issue.
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