It looks like you need PhinX (Photon in X) running in order to see the GUI in VNC.
https://forums.openqnx.com/t/topic/3245
https://sourceforge.net/projects/openqnx/files/
I have no idea if the version is the latest one since these posts are 15 years old now. It’s possible you need a newer version of PhinX and I have no idea where you’d get it now unless someone here has a copy.
Tim