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