// in my main.qml file
    //
    state: "splash"

    states: [
      State {
        name: "splash"
        PropertyChanges { target: splashScene; opacity: 1}
        PropertyChanges { target: starmapScene; opacity: 0}
      },
      State {
        name: "starmap"
        PropertyChanges { target: splashScene; opacity: 0}
        PropertyChanges { target: starmapScene; opacity: 1}
      }
    ]

    onStateChanged: console.log("HUD: switched to state '", state, "'")


    // in my splash scene
    //
    MouseArea {
        anchors.fill: parent
        onClicked: {
            if (gameWindow.activeScene === splashScene) {
                console.log("onClick called")
                gameWindow.state = "starmap" // let state transition handle opacity animation
                //splashScene.opacity = 0
                //starmapScene.opacity = 1
            }
        }
    }

    // I've tried this one and the transition
    //Behavior on opacity {
    //  NumberAnimation { duration: 10000 }
   // }

    transitions: [
        Transition {
            NumberAnimation {
                property: "opacity"
                easing.type: Easing.InOutQuad
                duration: 10000
            }
        }
    ]