Once you select the user to log in as
there's a dropdown menu (I forget what it's called I'm at
work) that lets you select your session type (Gnome/Wayland or
Gnome/Xorg) or whatever desktop managers you have installed.
Richard
That only shows "Gnome" or "Gnome Classic" on my system. Using a
pretty stock Fedora install, though it's been upgrade from two or
three previous releases to F27.