First thing in BIOS is to make sure you have all virtualisation settings ‘on’, and secure boot ‘off’, else it won’t install on bare metal or in a VM its the same, you have to enable virtualisation for the VM and secure boot off, for it to install in a VM as well.
VM install is simply not practical for most people, as it needs 120GB hard disk space (not too bad) and then 16 GB RAM for the virtual machine alone. (not so great unless you have a 24+ GB RAM in your physical machine
This is mainly due to the way Qubes works, essentially its a Zen hypervisor (a very light Linux based virtual machine host) and everything else is virtualised on top, this is also why there can be short delays between launching things and them appearing in ‘yet another’ VM device, when using qubes.
Personally I use my own VM and Tails if I want a fairly secure, anonymous system, on a reboot it is a clean system again. (remember though you might still want a random MAC for your network card in the physical machine to be unknown)