KWin is not supported on Kicksecure 18. See a recent forum thread:
You can configure additional workspaces in labwc, which can be switched between using a keyboard shortcut. See:
Unfortunately, LXQt’s desktop switcher widget does not work with labwc yet. It probably will in Kicksecure 19, but this is the best solution for the time being (unless we create a custom desktop switcher widget of our own sooner than that).