You could count anything that is depended upon (a node in the dependency tree) as a library and anything that isn'd (a leaf) an app.

Note that some end-usor applications are not "leaf" packages but nodes as they are both a library and an app (i.e. yt-dlp).

Maybe also add a criteria that they depend on X11, Wayland, (will still include libraries like java) or GUI toolkits like Qt or libadwaita/gtk.