Enabling no-subscription repositories

Prepare

Launch shell from hypervisor

This should provide root shell (priviledged access), if not elevate

sudo su

Ensure Internet connectivity from hypervisor itself (it can resolve and ping the source)

ping download.proxmox.com

apt update
apt install tmux

tmux

On Debian v13 (trixie)

mv /etc/apt/sources.list.d/pve-enterprise.sources  /root
mv /etc/apt/sources.list.d/ceph.sources            /root

Which version of Debian is running?

hostnamectl | grep -i debian

Create new file

nano /etc/apt/sources.list.d/pve-no-subscription.list 

repos

# for Debian GNU/Linux 13 (trixie)
deb http://download.proxmox.com/debian/pve trixie pve-no-subscription

close editor, confirm changes (save)

CTRL+X, y

Adjust Debian repos

nano /etc/apt/sources.list.d/debian.sources 

verify repos

#
# for Debian GNU/Linux 13 (trixie)
#

Types: deb
URIs: http://deb.debian.org/debian/
Suites: trixie trixie-updates
Components: main contrib non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Types: deb
URIs: http://security.debian.org/debian-security/
Suites: trixie-security
Components: main contrib non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Close editor, save

CTRL+X, y

Verify that repositories declared properly

apt policy

another one:

Do APT update

apt update

List packages ready for update, most important that there are new packages from PVE repo.

apt list --upgradable

another one:

Perform upgrade (when needed)

apt upgrade

the another one