The update to Qt Creator 16.0.0 and Qt 6.9.0 solved the problem. Thank you !

QtXmlPatters was dropped (for good reasons - unmaintainable), For the two others see https://www.qt.io/blog/qt-extras-modules-in-qt-6

when I rerun, I am told that QtWebView cannot contain more than one item, so I guess I cannot save a c++ class in QtWebView, going through the doc I found that the c++ classes I needed had already been extended to the quick module. So, I'm going to use the c++ classes in this module instead. Thank you very much for your help.

Solved using this answer on StackOverflow.

Forgive me if this doesn't help, but it's what I'm thinking. I'm not sure if this will even work (unsure if you can swap sources) like this on width changed... but onCompleted should be ok? It may get you experimenting / thinking differently to get a solution. http://doc.qt.io/qt-5/qml-qtquick-loader.html#source-prop Loader { id: container anchors.fill: parent // setSource on Loader Component complete Component.onCompleted: { doSetSource(); } } Connection { target: container; onWidthChanged: { doSetSource(); } } function doSetSource(){ if(container.width < 320) { container.setSource("ViewSmall.qml"); ...