Microsoft are forcing the move of the Outlook navigation bar to the top left from the bottom under mailboxes. You used to be able to reverse this by turning off “coming soon”. But that is no longer an option.

You can move this back to the bottom with a registry addition.

Close Outlook> open registry editor > In: Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\ExperimentEcs\outlook\Overrides

Add String Value called: Microsoft.Office.Outlook.Hub.HubBar

Edit and give value data: False

Open outlook and check moved back to bottom