The common problem is that using multiple Xscreens has “come out of fashion” so most if not all window managers/desktop environments have removed support for it, like gnome2,xfce3,kde3 supported this, gnome3,xfce4,kde5 don’t support this anymore.
You might check if switching to Mate helps with that, at least it was started as a gnome2 fork, so maybe this still supports multiple Xscreens.