I build a qcow2 image with docker environment on pve server just like u.
Building it in a docker environment will be a good choice.
wget https://raw.githubusercontent.com/vyos/vyos-vm-images/current/Dockerfile
docker run --rm -it --privileged -v $(pwd):/vm-build -v $(pwd)/images:/images -w /vm-build vyos-vm-images:latest bash
ansible-playbook qemu.yml \
-e disk_size=2 \
-e iso_local=tmp/vyos-1.3.6-amd64.iso \
-e grub_console=serial \
-e cloud_init=true \
-e cloud_init_ds=NoCloud \
-e guest_agent=qemu \
-e enable_ssh=true