I was trying to figure out if it was C++/CLI or C++/CX (I don't do enough Windows dev to know at a glance...). I was hoping it was C++/WinRT – I'm interested in seeing the new language projection in action.
Apparently C++/WinRt was only introduced in Windows 1803 [1], a few years after original Win 10. Interesting to learn that it was originally developed by an independent developer, who was then brought into Microsoft to continue work on it. C++/WinRt uses standard c++.
For an example of OS code that uses C++/WinRT, check out the native UI controls library, WinUI: https://github.com/Microsoft/microsoft-ui-xaml