Attached will be a small sample application that have a QDockwidget which contains a QOpenGLWidget. The dockwidget is floating and not visible. The calling render() on the MainWindow to retrieve a QImage and it produces the following warning:

"Asking for share context for widget that does not have a window handle
QOpenGLWidget: Cannot be used without a context shared with the toplevel."

Note that the QImage result is correct.