The Outlook 2019 Preview reveals how Microsoft want to inform people about new Office features after installing update. A new 'What's New?' panel will replace the current pop-up screen. It will list new and changed features, linking to a page to learn more.

You'll find it on the "Help" tab in the Ribbon menu, along with how-to guides that load within app.

Change Managers, leverage the new 'What's New?' panel as an education and awareness tool. 'What's New?" won't highlight why a new feature is useful in the context of your organisation or team environment. That's your role and the role of your change champions, to give a new feature context.  But 'What's New?' is a good starter to generic feature education.