# Proxmox by default updates from subscription based repo, for without subscription based repo update. We need to do some extra steps:

# Edit /etc/apt/sources.list ( add this )
$ vim /etc/apt/sources.list

# Not for production use
deb http://download.proxmox.com/debian buster pve-no-subscription


$ cd /etc/apt/sources.list.d
$ cp pve-enterprise.list pve-enterprise.list.bak
$ vim pve-enterprise.list
# comment out this line : deb https://enterprise.proxmox.com/debian/pve buster pve-enterprise

# Update the system
$ apt update

# Distro upgrade
apt dist-upgrade