I had the problem of Kdenlive just showing the splash screen and then it starts invisible.
I am using the Flatpak and I could fix this by deleting the file ~/.var/app/org.kde.kdenlive/data/kdenlive/kdenlivestaterc
Now the same problem occurs but that data file does not exist.
On closing the invisible Kdenlive winodw, the terminal shows:
QPaintDevice: Cannot destroy paint device that is being painted.
Kdenlive version 24.08.00, system Fedora 39.