Updated for Proxmox VE 7.4.
In Proxmox, we can enable updates via apt without a paid license.
Establish a shell on your Proxmox server. Replace pve with the hostname or IP address of your Proxmox server.
ssh root@pve
Temporarily disabled enterprise updates.
sed -i 's:^deb :#deb :g' /etc/apt/sources.list.d/pve-enterprise.list
Get non-subscription signing key.
wget http://download.proxmox.com/debian/proxmox-release-bullseye.gpg -O /etc/apt/trusted.gpg.d/proxmox-release-bullseye.gpg
Add the non-subscription apt source.
echo '# pve-no-subscription repository provided by proxmox.com, not recommended for production use
deb http://download.proxmox.com/debian/pve bullseye pve-no-subscription
' > /etc/apt/sources.list.d/pve-no-subscription.list
Update the local apt database and upgrade using pveupgrade.
apt update
pveupgrade