[Twinny]

You have to run graal4.exe with the additional option 'opengl'. Follow these steps for an easy solution.

Browser to your graal install directory (e.g. C:\Program Files\Graal\), right click graal4.exe and choose Send To => Desktop (create shortcut).

Close the window, right click the newly created shortcut and choose properties. In the target section, add -opengl at the end. Mine ended up with "C:\Program Files\Graal\Graal4.exe" -opengl

Finally rename the shortcut to something appropriate (e.g. Graal Opengl). Now when you want to run graal in opengl, just use that shortcut.