Let me guess, you “need” a more sophisticated UI toolkit on mobile? ;-p

With Qt Widgets you’ll have to go out of your way to make it work nice with touch devices, since it has been created for desktop usage with mouse and keyboard input in mind, while Qt Quick has been made with mobile user interfaces in mind.

I wonder why you’re worried about the performance of Qt Quick. It has hardware rendering by default and the layout system is designed with applications in mind, unlike HTML, which tries to retrofit a document markup language into an application markup language. Additionally, QML and JavaScript files can be precompile to native code, if the JIT compilation of QML and JavaScript files would be a performance concern.

QML just sits in this sweet spot of being easy to use for developers while not consuming too much ( Electron-levels) of system resources. Of course, if you abuse QML you can most definitely create slow applications in it, but you could say that about every framework.