How to deal with QML-based Qt6

[tio-trom]

From my tests one needs to add the export QT_QUICK_CONTROLS_STYLE=gtk2 variable in order to theme the QML-based QT apps. Works for QT5 but for QT6 it will make the apps fail to launch the GUI with errors like:

[Warning] (Thu Sep 28 04:14:09 2023): QQmlApplicationEngine failed to load component
[Warning] (Thu Sep 28 04:14:09 2023): qrc:/gpt4all/main.qml: module "gtk2" is not installed
[Warning] (Thu Sep 28 04:14:09 2023): QIODevice::read (QNetworkReplyHttpImpl): device not open
[Warning] (Thu Sep 28 04:14:09 2023): ERROR: Couldn't parse:  "" "illegal value"

What's the solution?

Thanks