UWP was introduced in Windows (Phone) 10. Prior to that, apps could share backend code between Windows 8 and Windows Phone 8, but the UI had to be developed sep

UWP was introduced in Windows (Phone) 10. Prior to that, apps could share backend code between Windows 8 and Windows Phone 8, but the UI had to be developed separately for each. The Windows Phone 8 to 10 transition lost a lot of people, myself being one of them. There are very few Windows Phone 10 handsets being produced, especially if you are looking for "flagship" quality.