Desktop Environment    How to install Kde, Gnome and Xfce.   KDE Plasma You can install the meta or the plasma group Install sddm it is kde's display manager 
 $ sudo pacman -S plasma kde-applications sddm for meta
 sudo pacman -S plasma-meta kde-applications-meta sddm to start up plasma 
 sudo systemctl start sddm.service to always use sddm on bootup 
 sudo systemctl enable sddm.service Start kde from xorg 
 startx
 exec startplasma-x11 
  Gnome 
 $ sudo pacman -S gnome gnome-extra  to start up Gnome 
 sudo systemctl start gdm.service to allways use gdm on bootup 
 sudo systemctl enable gdm.service Start Gnome from xorg 
 startx
 exec gnome-session
 Xfce 
 $ sudo pacman -S xfce4 xfce4-goodies  to start up Xfce form a display manager Start Xfce from xorg 
 startx
 exec startxfce4
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