Ooh, this is interesting. Zac Bowden somehow got hold of unfinished builds of Project Andromeda from just before it all got cancelled. Remember, this was the evolution of Windows 10 Mobile with latest kernel and plenty of UI ideas from the world of journalling. It ran UWP applications and would have been fully compatible with everything in Windows 10 Mobile - and you'll see that many app screens and settings look identical. The key thing here is a modern UI overlay that understands Project Andromeda's two displays, along with a homescreen that's more of a blank canvas, designed to be drawn on with a Surface Pen. All somewhat revolutionary and, as Zac says, horribly behind schedule mid-2018, with the finished OS and device due to ship at the end of the year.
The decision was therefore made by Microsoft to cancel Project Andromeda, scrap the journalling ideas, and to build the multi-screen UI on top of Android 10, all of which emerged in the original Surface Duo.
Here's Zac's video, grab a coffee and sit back(!), he does a great job of explaining it all and you'll want to watch all of it.
In a world of iPhones and Android, and even with a groundswell of Lumia fans inbound, I'm not sure about the canvas-as-homescreen approach. There's simply too much to launch and keep track of in modern smartphones. Perhaps for the ultra creative, perhaps for minimalists, it might have found its place. I suspect that, as with the Duo and Duo 2 themselves, you'd have to live with them in order to appreciate the different approach needed to make the most of the unique form factor.