What about 'unattended-upgrades' in Debian?
This way you can configure to install automatically security (only security, or more) updates but I'd not configure it for automatic reboot on a promox box.
This way it will install all updates automatically and you get a notification via mail what was installed - and in case of a kernel update,
you will only need to reboot. - It won't tell you explicitely but you will you will know what was installed and can decide if you want to reboot.
Don't forget to create a 10periodic file in /etc/apt/apt.conf.d additionally to modify 50unattended.
(I had just imagined KSplice uptrack on Proxmox would be a awesome combination, but it's now gone Oracle :-/