Too bad Ubuntu and Debian repositories carries old version of Wayland.
So on what does GDM run?
Does GDM run on X, then you select the Wayland session, then you run both X and Wayland?
Or does GDM run on Wayland?
Or does GDM run on X then X exits and Wayland starts?
Or GDM runs on framebuffer or something independent of both X and Wayland?