When Qt.ExpandedClientAreaHint and  Qt.NoTitleBarBackgroundHint is set it blends client area to titleBar very nicely with native min/max/close button. But you can not drag the window from the area of titlebar Since native buttons are there it is intuitive that it will also drag

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
id: mainWindow
visible: true
width: 900
height: 600
color: "lightblue"
flags: Qt.ExpandedClientAreaHint | Qt.NoTitleBarBackgroundHint
}