Hi @Anonymous ,
Thanks for reaching out! As per my understanding you are trying to fetch all the users' details who are reporting to specific manager. For this scenario, there is a direct API available which will give you the all the users who has manager specified in the request URL/endpoint.
Get the reports for the manager userPrincipalName.
https://graph.microsoft.com/v1.0/users/{managerUserPrincipalName}/directReports
Document reference: https://learn.microsoft.com/en-us/graph/api/user-list-directreports?view=graph-rest-1.0&tabs=http
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