Which is basically the same thing. Gnome uses Mutter, which is a part of the Gnome project as a whole.

Wayland changes things a fair bit compared to Xorg. There's no standard Wayland server, each DE implements their own to suit their needs. Some libraries have emerged to help with that, it's relatively easy to get going with wlroots which Sway/Hyprland/Gamescope uses. But Gnome makes their own and so does KDE so it can integrate more deeply with the DE.

There's non-desktop compositors too, like for VR for example where you can manage your windows in 3D space all around you. That's where Wayland shines, that gets super complicated to do in Xorg but a breeze with Wayland.