[Windows] Titler tool, display real background not working in "directX" backend.

here a forum report about this: https://forum.kde.org/viewtopic.php?f=265&t=165283 to see the correct background is necessary to switch the backend to OPENGL.

similar to issue: https://invent.kde.org/kde/kdenlive/-/issues/596

opened also a request to make the OPENGL backend the default on Windows before release 20.04 to prevent issues: https://invent.kde.org/kde/kdenlive/-/issues/604

Edit [ME]
same here: https://bugs.kde.org/show_bug.cgi?id=423922, https://bugs.kde.org/show_bug.cgi?id=425088