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I recommend you not use setContextProperty, as it adds your Python classes to the QML global namespace. IIRC it was the first way to interface C++ classes with QML (at the time the API was created. Now you can access it in python). Better is to use more automatic registration available now.
Any python classes you wish to expose to QML, annotate the class with @QmlElement
https://doc.qt.io/qtforpython/PySide6/QtQml/QmlElement.html
This will automatically register the class as a QML type.
Then, in QML you can create an instance of the python class using
MyPythonClass {
id: foo
}
And use it like any other QML type.