I use two identical monitors, and KDE is flawless in that regard.
I don’t use Wayland because it does not let me use xeyes. Until someone comes up with an xeyes alternative that works on Wayland, I consider Wayland to be completely unusable, regardless of the DE. So, at the moment, I don’t care about feature-completeness of KDE on Wayland.
One has to have priorities in life: xeyes > feature-complete KDE on Wayland
