Outlook is getting an overhaul for Mac. The verge reported on it on the 4th. https://www.theverge.com/2019/11/4/20942050/microsoft-outlook-mac-new-design-features-performance-improvements-update-ignite
You can use "com.microsoft.Outlook" Key: EnableNewOutlook Data Type: Integer
However, the only possible values are: 0 = Switch hidden (default)
1 = Switch displayed, default off
2 = Switch displayed, default on
3 = New Outlook enabled with switch hidden
In our case where the "New Look" has issues with Shared Maibloxes and some Security Software we really need: 4 = New Outlook disabled with switch hidden