Two things to change and you are good to go if you start with the dev github and want xfce4.

We change the content of packages.x86_64 and remove alci-dwm-nemesis.

A few lines down we have already a desktop – xfce4 and xfce4-goodies.
Change the packages if you want gnome, deepin, plasma, etc.

Then we tell SDDM that it should up with a certain desktop in this file