It’s likely that your phone can do almost everything Windows 10 can do. So what is the point of your desktop? It used to be that you need the desktop because it is more powerful than your phone. Instead of owning the desktop OS market, Microsoft is now trying to compete with Android and IOS, where they are weak.
If I were CEO of Microsoft, I would focus on making Windows do things on the desktop that phones can never do. Take advantage of the big screen and big processing power. Capitalize on the peripherals.
Instead of pasting cheesy Twitter and Candy Crush Saga apps onto the Start menu, I would offer powerful 3D modeling apps, photo editing apps, programming compilers, massive databases, number-crunching analysis apps, etc. The apps I would provide would be too big and too powerful to duplicate on a phone or tablet. I would put a supercomputer on your desktop.
The large screens of desktop computers are also a feature that phones cannot duplicate. Take full advantage of them. Make the screen a wonderland of eye-popping graphics. Use the screen real estate to let people visualize data and manipulate it in ways an iPad cannot because it is too small.
Finally, I would go the route of Nintendo and design all sorts of peripherals that would only work with Windows computers. Imagine attaching devices like electric guitars, bike pedals, sound systems, 3D printers, or ultrasound wands to your computer and having them work seamlessly with Windows. Now that’s something your smartphone or tablet cannot do.