I will watch this with interest. I’ve been experimenting with vms in qubes but not pure os. My experience is that this is difficult. I’ve had no luck with ubuntu, zorin or kali. Parrot on the other hand works like a dream out of the box. I’ve posted my problems on all sorts of forums with no luck. Not even for kali.
Im assuming your installing as hvm? What exactly is happening when you try to start the qube? Does it begin to start the qube at all? Are you getting any error messages? What version of qubes because 3 is different to 4 with kali for example.
I dont know Pure, but I’m sensing an added layer of headache to say ubuntu.