Hi. THIS IS A SERIOUS BUG RUNNING THROUGH 5.15 (NOT TESTED IN EARLIER VERSIONS) - 6.8. In a nutshell, the steps to reproduce are as follows:

1. To create the simplest Quitquik Apulikation project, copy the following code into your Main.qml program:

import QtQuick
import QtQuick.Controls.Basic

Window {
    id: _app
    width: 640
    height: 480
    visible: true
    title: ""
    flags: Qt.Window | Qt.FramelessWindowHint
    color: "#00000000"

    Rectangle {
      width: 600  
      height: 440
      anchors.centerIn: parent

      Row {
	Button {
	  text: "Min"
    	  onClicked: () => {
            _app.showMinimized()
          }
	}
      }
    }
}

2. Run the program, click the customized minimize button, and then tap the taskbar to restore the program, look at the top left corner of the form.

3. You'll see that there's a cyan rectangular area in the upper left corner, and the title of the program is displayed, which I didn't set anymore. This is unexpected. At least the cyan rectangular area should not be displayed, and the title should not be displayed. And if you look closely, there's something behind the unknown cyan area.....

4. Expected behavior: The title should not be displayed and cyan areas should not appear. There shouldn't be anything behind an unknown cyan area.

Alternatively, you can refer to the Qt forum discussion on this issue. [qml-6-bug-on-window-restore-from-task-bar|[Qml 6 Bug on Window Restore from Task Bar | Qt Forum|https://forum.qt.io/topic/156420/qml-6-bug-on-window-restore-from-task-bar]]