The problem with Qt is that it draws its own widgets. It is close on some platforms like with Gtk+ theme, but most people report how it does not look native on their platform. Also on Android it has to use JNI and NDK so it's not native to Android as DEX/Java is. On Windows I believe that CLR or at least COM (you can do it even C, but that requires effort) is a native platform.

Qt is from a time when C was kinda native for everyone. It's a different world now for better or worse.

Of course Qt has some advantage over one of many other widget toolkits drawing their own widgets. It hooks to native accessibility APIs for example. Other than that: dlangui, Lambda Native or even SDL2 can be seen as contenders.