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

Ooohhhhh...shiny! Thanks!

Is it possible to control this setting (New Outlook) for users?

Yes, https://techcommunity.microsoft.com/t5/video-hub/the-new-outlook-for-mac-under-the-hood/m-p/1681528 covers that

Awesome, thank you for that @Chris

@Chris yes and no...

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