Can't set palette for Window

Qt's documentation says there's a property called "palette" in Window, and it was introduced in Qt 6.0, however, when I was trying to set a QPalette to it, the QML engine warns about "palette" is a non-existent property and failed to load the component.

import QtQuick

Window {
    width: 640
    height: 480
    visible: true
    palette.mid: "purple"

    Rectangle {
        anchors.fill: parent
        color: palette.mid
    }
}