I am trying to install Ubuntu Core 20 as a VM (not a CT). I followed a guide here;
https://blog.viktorpetersson.com/2019/10/03/ubuntu-core-on-proxmox.html
As I am using Ubuntu Core 20, I did this;
wget http://cdimage.ubuntu.com/ubuntu-core/20/stable/current/ubuntu-core-20-amd64.img.xz
unxz...