Upgrade Proxmox & Debian to "bookworm"

Proxmox & Debian

open console as root or sudo su aka su - and make sure the system is updated

apt update && apt upgrade -y

after updating the system repeat upgrade to check if there are packages for removal and performe cleanup by doing

apt autoremove

Proxmox only

perform the upgrade check

pve7to8

this will check if there are issues to solve before updating e.g. shutdown running VM´s

If it fails with

simply install the hold back package proxmox-ve manualy and run the check again

apt install proxmox-ve

Proxmox & Debian

update your sources list to "bookworm"

sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list

and perform update and dist upgrade

apt update && apt dist-upgrade -y

you can confirm configuration changes with enter which will result in keeping curent config file e.g.:

Installing new version of config file /etc/debian_version ...

Configuration file '/etc/issue'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** issue (Y/I/N/O/D/Z) [default=N] ? 

as well as restarting services during update

if everything went fine do a last

apt autoremove

and reboot server

reboot