FWIW, here is a patch which causes Emacs to check that at least one of the environment variables WAYLAND_DISPLAY, DISPLAY, BROADWAY_DISPLAY is set before it will try to use PGTK for its initial window.

This patch is not suitable for merging, because it doesn˘t consider what happens if you try to use PGTK on Windows or MacOS.  However, people might find it useful if they˘re not using one of those platforms.

This patch depends on the patch for bug 72118.

-- 
Peter Oliver