Complex sentence: GNOME runs on the X Window System and as of GNOME 3.10 also on Wayland as of GNOME 3.22 Wayland is the default.
Split into simpler sentences: GNOME runs on the X Window System; beginning with GNOME 3.10, support for running Wayland as an alternative display server was added. As of GNOME 3.22 Wayland is the default.