Updated for Proxmox VE 9.
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
Remove the enterprise repository files.
rm /etc/apt/sources.list.d/pve-enterprise.sources
rm /etc/apt/sources.list.d/ceph.sources
Get the Proxmox archive keyring.
wget https://enterprise.proxmox.com/debian/proxmox-archive-keyring-trixie.gpg -O /usr/share/keyrings/proxmox-archive-keyring.gpg
Add the no-subscription sources.
cat > /etc/apt/sources.list.d/proxmox.sources << 'EOF'
Types: deb
URIs: http://download.proxmox.com/debian/pve
Suites: trixie
Components: pve-no-subscription
Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
EOF
cat > /etc/apt/sources.list.d/ceph.sources << 'EOF'
Types: deb
URIs: http://download.proxmox.com/debian/ceph-tentacle
Suites: trixie
Components: no-subscription
Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
EOF
If you prefer the ceph-squid release, replace ceph-tentacle with ceph-squid in the URI above.
Update the local apt database and upgrade using pveupgrade.
apt update
pveupgrade