на какой бы версии мы не находились, нам нужны некоторые манипуляции
pve6to7 vim /etc/apt/sources.list deb http://ftp.ru.debian.org/debian bullseye main contrib deb http://ftp.ru.debian.org/debian bullseye-updates main contrib deb http://security.debian.org bullseye-security main contrib deb http://download.proxmox.com/debian bullseye pve-no-subscription apt update apt dist-upgrade N N reboot
pve7to8 vim /etc/apt/sources.list deb http://ftp.ru.debian.org/debian bookworm main contrib deb http://ftp.ru.debian.org/debian bookworm-updates main contrib deb http://security.debian.org bookworm-security main contrib deb http://download.proxmox.com/debian bookworm pve-no-subscription apt update apt dist-upgrade /etc/issue N /etc/lvm/lvm.conf Y /etc/ssh/sshd_config Y /etc/default/grub N reboot