Still no luck here either.
As it happens, my desktop is running Hirsute (Ubuntu 21.04) and seems to be at a similar level of functionality (Wayland, gnome-remote-desktop) - and VNC does work - at least to the point of seeing something listening on port 5900.
On the other hand, even though I start the service on the Librem 5 and journalctl shows that the service started, I don’t see anything listening on that port.
I have attempted to replicate the configuration information on the Librem 5 (specifying what connections VNC will listen on and specifying the password), the things that the “settings” app allows me to configure for the VNC server on the desktop.
It may be worth revisiting once Byzantium is released.