Ah I haven't been checking OccluderPolygon2D, however this doesn't seem to be what
E 0:00:01.168 canvas_light_occluder_attach_to_canvas: Condition "!occluder" is true.
It would normaly take a RID returned by
VisualServer.canvas_light_occluder_create(), however I would still like to use the the scene and node GUI instead of having to create everything from code.
It seems this is currently not possible, sadly. Thank you anyways though.
Edit: Do you think a pull request adding get_rid() for those resources would have chance of being accepted?