1 - Qt is not an OS SDK. Apparently you missed that part of my comment.
2 - Qt has been migrating away from pure C++, again you also missed pure from my comment, modern Qt applications are written in Qt Quick, a JavaScript dialect, with underlying components written in C++.
C++ Widgets have hardly changed since Qt 4, other than being updated to the underlying Qt infrastructure.
Again, read my comment, very carefully, then you migth get it.
Afterwards go learn how to create a GUI for macOS, iOS, Android, ChromeOS, Windows, WebOS (as shipped by LG) or even Fuchsia, using only their SDKs and nothing else.
As for Qt not moving away from pure C++, go use it with pure C++ on iOS, Android and embedded devices.
> Afterwards go learn how to create a GUI for macOS, iOS, Android, ChromeOS, Windows, WebOS (as shipped by LG) or even Fuchsia, using only their SDKs and nothing else.
Why use native SDK when there is QT?
The same can be said for Java. Why use Swing when there is native SDK?
2 - Qt has been migrating away from pure C++, again you also missed pure from my comment, modern Qt applications are written in Qt Quick, a JavaScript dialect, with underlying components written in C++.
C++ Widgets have hardly changed since Qt 4, other than being updated to the underlying Qt infrastructure.