By "workspaces" do you mean what KDE calls "Virtual Desktops"? AFAICT, no, they don't seem to be changeable per-monitor. Additionally, when I was poking around

By "workspaces" do you mean what KDE calls "Virtual Desktops"? AFAICT, no, they don't seem to be changeable per-monitor. Additionally, when I was poking around in the System Settings to see whether there was some option for that, I enabled "Show animation when switching" -- and then half of my monitor froze!!! :-D So "less jank" is relative, ha ha...