Looks like there is a regression vom 6.5.2 => 6.6.0. When disconnecting an external standard resolution monitor, using the MacBook retina display instead, the window content is not correctly scaled. Please see the attached screenshots.

This does not occur when using both displays and dragging the window between them.

Works with 6.5.2.

import QtQuick
import QtQuick.Window

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World Qt 6.6")

    Rectangle {
        color: "yellow"
        anchors.fill: parent
    }
}