Xorg-server shows black screen on Cubietruck, how to fix?

Question

X.Org

Installed Armbian Bionic 5.3 on Cubietruck.
By default, it boots into console mode.
I installed KDE (apt install kde-full) and X (apt install xinit xorg-server)
After running "startx" the screen is black, although from another console I see that all the necessary processes (X and KDE) have started and are working

How to get a normal Xorg work?

On an older Armbian distribution (with Linux 3.4 kernel), Xorg worked fine.

PS. It would also be nice to run Wayland instead of X, but that's another story.