QOpenGLWindow::grabFramebuffer() returns flipped imaged *sometimes*

[375gnu]

I have an application which uses Qt5/Qt6. On some hardware (e.g. Intel) QOpenGLWindow::grabFramebuffer() returns vertically flipped image, while on other (Nvidia) it returns a proper image. On the other hand in when the application core uses GLES then on Intel I have a proper image as well.

Qt is used for interface only so all matrices are set by the applications and the assume flipped Y axis. We also have other interfaces (e.g. Gtk and WinAPI) and with them everything works fine everywhere.

How can I make QOpenGLWindow::grabFramebuffer() always return images in the same orientation?