When I try to share my screen (using the Screen native client, running Awesome as my Xorg wm on Debian), I get a black screen (with a green sharing border; others in the session also see black). The only way to recover is to type blind, open a terminal, and kill Screen.
If I switch from an Awesome Xorg session to gnome, screen sharing works. Not sure if the issue is Wayland-related or the presence/absence of some Gnome-related service, but Screen should at least detect this pathological situation and provide a helpful error message rather than leaving us in the dark!