Can I ask how you managed to set a different scale factor for each screen? In the system settings I can only find a global scale factor... Or is this only supported using Wayland?
KDE on wayland supports it natively, on X11 you could set the environment variable QT_SCREEN_SCALE_FACTORS, but this will only affect Qt/KDE applications, not Gtk/Gnome applications
I don't think X is so limited. You can use the xrandr tool to set pretty much arbitrary positioning and scaling for each screen, at least with the proprietary NVidia drivers.
