Hi @Said Amchart ,
Could you perform the same test on your side and confirm if this is the default behavior? maybe a bug?
I tested in my lab tenant, and everything is fine from my side. See the screenshot below, user1 shared the folder Test with user2, and user2 can search within the shared folder as expected:
Noticed from the issue history in the Service Health dashboard of Microsoft 365 admin center that there was apotentially relevant issue "Users may be unable to perform searches in delegated mailboxes via Outlook on the web" (EX494607) and its current status is "Service restored". Would you have a check again to see if it's working now on your side?
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