If you see a notification within Outlook indicating that an add-in is slowing down Outlook start up or not working as expected, try the following:
In Outlook, click on File in the top left-hand corner to display the Account Information.
Click on Manage COM Add-ins > Slow and Disabled COM Add-ins
This will open the Add-ins window.
Expand Options under the add-in that is causing the issue (possibly Teams add-in) and tick the box Always enable this add-in.
Click Apply then close the window.
Click Apply then close the window.
Close and relaunch Outlook.