If you don't want to pay for a Proxmox subscription you can still get updates through the no-subscription channel.
cd /etc/apt/sources.list.d cp pve-enterprise.list pve-no-subscription.list nano pve-no-subscription.list
Edit the pve-no-subscription.list to the below
deb http://download.proxmox.com/debian/pve bookworm pve-no-subscription
Run updates, but only use dist-upgrade and not regular upgrade as it may break dependencies.
apt-get update apt-get dist-upgrade