Universal Windows Platform (UWP) is an initiative that Microsoft announced a few years ago, allowing developers to create apps that run across a variety of Windows devices including HoloLens, Windows 10, Xbox One, and more, without requiring full code re-writes. However, as we know, the company has recently transitioned focus to a new approach where the Microsoft Store accepts any app including Win32, regardless of the packaging and technology being used. This has fueled ongoing speculation that UWP is on the way out, and today, Microsoft has officially published guidance about how to migrate away from UWP.
The new documentation was highlighted by Rafael Rivera over on Twitter. In it, Microsoft has noted the advantages of the Windows App SDK, touting that it offers the latest features which are decoupled from the OS, compatibility with .NET 5, a faster release cadence, and backward compatibility till Windows 10 version 1809, among many other things. Most Windows Runtime (WinRT) APIs are supported in Windows App SDK via WinUI 3 Library and WinRT COM interfaces. You can find more details about this here.
While the documentation is very developer-focused since it talks about migrating backend technologies - and you can read it in detail here -, perhaps the more interesting questions it raises is regarding the future of UWP. The compute platform definitely isn't dead right now because developers can still use it to build apps if they don't need the added benefits of Windows App SDK, and in a separate announcement on GitHub, Microsoft has clarified that "Windows SDK will continue to support UWP project types, including bug, reliability, and security fixes". However, developers who want to take advantage of the latest features are being clearly recommended to migrate to Windows App SDK as it does not seem that UWP will receive any meaningful feature updates moving forward.
At the end of the day, the announcement doesn't indicate a huge change for end-users. It's mainly intended for developers who are building apps for Microsoft platforms, and based on the latest guidance, it appears that they will need to consider several things before they choose a compute platform. That said, Windows App SDK has been highlighted as the clear strategic direction from Microsoft as it combines the capabilities of Win32 desktop apps as well as UWP.