Outlook group by flag status

What's the type of your account(Exchange/POP/IMAP)?

If it's an Exchange or a POP account, as I know, we can easily flag the emails (right the email>Follow Up>No Date) you need to pin on the top of Inbox, and then select Filter: All Mail and Arranged by: Flag Due Date. Then the emails flagged will be placed on the top of Inbox.

If it's an IMAP account, it's suggested that you could achieve pinning the emails on the top of Inbox by flagging messages and changing the view. For specific steps, please refer to:

1.Flag the emails you want to pin on the top of Inbox;

2.Turn off the reading pane;

3.Click the flag icon to sort by the flag column;

4.Turn on the reading pane and save this view and rename it as Pin(View>Change View>Save Current view As a New View… );

In this way, the marked message will be placed on the top of Inbox, and then when you continue to mark the message later, it will be placed on the top.

Hope the above help!