title: QML items are not rendered
body: <p>Interesting problem with QML. When I create a default Qt Quick application and run it, I get a black screen. Window and other items are not rendered at all. But when I minimize it and return it to previous state again, then items are rendered. So does anyone know about this kind of problem?
  <a href="https://i.stack.imgur.com/QzBLm.png" rel="nofollow noreferrer">Before minimizing</a>
  <a href="https://i.stack.imgur.com/Rd2ll.png" rel="nofollow noreferrer">After minimizing</a></p>
  <p>In a very similar case (for another user), the window was being created, but none of the items were being rendered. In this case the window was completely blank (white) instead of black.
  The system was a Windows 10 with Qt 5.15. This issue was not appearing on non-Windows system.<br />
  (The solution was related to OpenGL. See details below.)</p>
  <pre><code>import QtQuick 2.5
  import QtQuick.Window 2.2
  
  Window {
      visible: true
      width: 500
      height: 500
  
      Rectangle {
          id: test
          width: 300
          height: 200
          color: &quot;red&quot;
          border.color: &quot;black&quot;
          border.width: 4
      }
      
      Rectangle {
          width: test.width / 2
          height: test.height / 2
          color: &quot;red&quot;
          border.color: &quot;black&quot;
          border.width: 4
          anchors.centerIn: parent
      
          Rectangle {
              width: parent.width / 2
              height: parent.height / 2
              radius: width * 0.5
              //x: 200
              //y: 200
              color: &quot;green&quot;
              border.color: &quot;darkgreen&quot;
              border.width: 4
              anchors.left: parent.left
              anchors.bottom: parent.bottom
          }
      }
  }
  </code></pre>