Since Microsoft release "Windows UI Library" or WinUILib. I want my app to use it as soon as possible.
But I'm wondering if you can use it and ship the app with it, even though the WinUILib is still in a pre-release state?
Is Microsoft store allow an app with a pre-release NuGet package?
Technically yes you can use it and publish your apps because controls of winui are already being used in official store apps so you will be fine. Preview only means that it is open for community feedback and will be stabilized probably with release of red stone 5 of windows 10 in october.