Download CentOS 8.4.2105 generic cloud image and then upgrade.
curl https://cloud.centos.org/centos/8/x86_64/images/CentOS-8-GenericCloud-8.4.2105-20210603.0.x86_64.qcow2 -o centos.qcow2
virt-customize -a centos.qcow2 \
--run-command "sed -i 's/^mirrorlist/#mirrorlist/g' /etc/yum.repos.d/*.repo" \
--run-command "sed -i 's|^#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|' /etc/yum.repos.d/*.repo" \
--update --selinux-relabel