Can a Windows 10 app built on the Universal Windows Platform (UWP) be ported back to Windows 7 customers? In particular, one made using XAML?
The UWP platform is only available for Windows 10 devices. We can't port it back.
If you want to use it on Windows 7 device. You can make a WPF, which use XAML, the same as UWP. And WPF can run on Window 7. Particular XAML and C# code can be reused.