Using New Outlook on Windows for professional communication and productivity
Dear Rajesh Bhandari,
Based on the behavior described, this is by design in New Outlook rather than an issue with your Outlook installation. Unlike the experience you may be familiar with in Classic Outlook, you can add the shared mailbox directly to the folder pane in New Outlook.
To do this, open New Outlook, then right-select your account name in the left-hand folder pane and select Add shared folder or mailbox. Enter the name or email address of the shared mailbox and add it. The shared mailbox will then appear in the folder pane, where you can expand it and access its folders.
I hope this helps clarify the situation. Greatly appreciate again for your patience and understanding.