Where are Settings and Customization in the latest version of Dynamics 365 v9.1?

In version 9, Microsoft introduced the new Unified UI, a new look and feel for Dynamics 365.  It was still possible to navigate to the “Classic” UI by switching to the Dynamics 365 – custom app.  With 9.1, this app has been removed!

Beginning in 9.1, to navigate to Customisation, Settings etc, click on the settings cog at the top-right of the screen and select “Advanced Settings”