@Sunil A M , When you list the user details using Microsoft Graph API, it doesn't list the memberOf details in that response. hence even if you apply the select filter with memberOf, it would always give you null.
If you want to list the groups the user is a part of you would have to use the following Microsoft Graph API:
GET https://graph.microsoft.com/beta/users/**{username/upn}**/memberof
you can get more details on this here: https://learn.microsoft.com/en-us/graph/api/user-list-memberof?view=graph-rest-1.0&tabs=http
Hope this helps.
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