the below code gives the error:
Cannot assign to non-existent property "onContentDataChanged"
and it expected can works without error as it is a valid property, it shall have an onPropertyChanged signal.
https://doc.qt.io/qt-6/qml-qtquick-controls2-popup.html

    Dialog {
        Text {
            text: qsTr("text")
        }
        onContentDataChanged: {
            console.log(contentData)
        }
    }

the below code can run, but the onContentChildrenChanged never triggers.
it is expected triggered once because there is visual children's item inside it.
and value of contentChildren shall be one Text item.

    Dialog {
        Text {
            text: qsTr("text")
        }
        onContentChildrenChanged: {
            console.log(contentChildren)
        }
    }