I have Kubuntu 18.10 with KDE Plasma v 5.14.4

When I go to System Settings->Appearance->Workspace Theme I get "The module Workspace Theme is not a valid configuration module", with diagnosis: "The desktop file settings-appearance-workspacetheme.desktop" does not specify a library. The file itself is there, but I need help in how to configure it.

In a somewhat related question - I have a new 34" widescreen monitor. I know KDE Plasma can configure desktops on multiple monitors, but ... is it possible to configure splitscreen/multiple desktops on a single monitor?

Thx, Gus