Here are some steps you can try to resolve the issue:

  1. Check Your Account Settings:

    • Open Outlook.

    • Go to File > Options > Advanced > Send/Receive.

    • Click on the Send/Receive button, then click Edit.

    • Find your account and uncheck the option “Get folder unread count for subscribed folders.”

    • Under Received mail items, check the option “Use the custom behavior defined below.”

    • In the window that displays your IMAP folders, select Inbox and leave the others unchecked.

    • Click OK and then exit out of options.

    • Perform a send/receive to test if there’s any improvement.