Blank screen, booting from GPU
Along with many others, it appears I am having the same issue.
I have been able to successfully install and run the Catalina VM through VNC, but now I am trying to setup the GPU passthrough and getting just a black screen when it boots.
I have removed the topolgy line from the XML, changed the network access, and made sure to reinsert the script at the bottom of the XML per @SpaceInvaderOne video.
Looking through the forum I can't seem to find any solution that has worked for anyone else, but perhaps I have just overlooked something?
CatalinaXML.txt