Earlier quoted context omitted.
Sadly instead of having native apps we have "web" monstrosities... each sporting custom "fancy" UI instead of following the OS native style…
Because WinUI and QT are so glamorous and offer a super intuitive development experience. /s
As for WinUI 3, apps are supposed to bundle it, so if you target Windows 11 and run the app on Windows 10, it'll look all rounded and drop-shadowy instead of flat like native Windows 10 apps. Great stuff.