Hello @jLight · You can use below calls for this purpose:
Users by name: In this scenario, you search for a specific user by name, which enables you to evaluate the lastSignInDateTime: https://graph.microsoft.com/beta/users?$filter=startswith(displayName,'markvi')&$select=displayName,signInActivity
Users by date: In this scenario, you request a list of users with a lastSignInDateTime before a specified date: https://graph.microsoft.com/beta/users?filter=signInActivity/lastSignInDateTime le 2019-06-01T00:00:00Z
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