well, good news bad news.
I got it to work, first try, which is both good and bad news.
Here is what I did on a fresh install step-by-step on Ubuntu 24.04.
I didn’t have to virsh edit, hide the hypervisor or do any tweaking at all. I did literally everything through virt-manager.
I am sure that this is probably going to need more tweaking for best performance but uh… no code 43?
So I am going to keep digging with you to get to the bottom of it 
Any deviations from what you did that you spot in what I did?