Hi Kesava Chenna,
Thanks for reaching out to Microsoft!
Currently, the Microsoft Graph API does not support list all the shared mailboxes. However, there is an existing feature request for this functionality. We encourage you to upvote this feature request on the Microsoft feedback portal. Your support will help prioritize this enhancement for future updates.
You can upvote the feature request here: Microsoft Feedback Portal.
Similar posts: https://learn.microsoft.com/en-us/answers/questions/1168052/can-i-get-a-list-of-all-shared-mailboxes-folders-u
Hope this helps.
If the answer is helpful, please click Accept Answer and kindly upvote. If you have any further questions about this answer, please click Comment.