Created attachment 115133 [details] Screenshot of touchpad KCM on Plasma 5.13.90 ... and synaptics is not.
The screenshot shows definitely libinput based, but on X11. The `new' touchpad UI is available only on Wayland. Please check and confirm your display server.
It is Xorg session, but I was told to report it anyway https://bugs.kde.org/show_bug.cgi?id=398710
Darn, I could have sworn that we had already fixed this. :/ *** This bug has been marked as a duplicate of bug 387153 ***