Haven’t tried Felgo so cannot comment properly as that framework is built on top of Qt/QML so overhead might be expected since it gives you additional features.

I could be very hard on this topic, in general this will depend on your app design and architecture since Qt made a number of improvements on the framework with each release, so if you try to do too much or badly, no framework will help.

Also read on Qt docs, as always, to get info on how to get 60FPS with QML and note that Qt uses separate rendering thread when possible which is a big advantage— https://doc.qt.io/qt-5/qtquick-visualcanvas-scenegraph.html.

So in conclusion, yes, your Qt/QML app is expected to work buttery smooth on Android/iOS!