It's not possible to compare the screen property of a Window with a screen from e.g. the Qt.application.screens array.

To reproduce, run the following example and move the window between two screens.

import QtQuick 2.12
import QtQuick.Controls 2.12
import QtQuick.Window 2.12

ApplicationWindow {
    id: window
    width: 400
    height: 400
    visible: true
    onScreenChanged: print(screen, Qt.application.screens[0])
}

Even though they are the same screens, the QQuickScreenInfo objects are different. A workaround is to compare the names of the screen.

In addition, the screen property returns a new QQuickScreenInfo object each time it's called, which seems wasteful.