Specifically, a dedicated server running Debian 12.
After a monthly sudo apt upgrade? (Is a monthly upgrade even necessary?)
Never? (unless there is a security update?)
Edit: I may be missing kernel upgrades. Those are probably good... I can't remember if I installed a LTS kernel. I imagine it would be unsecure to post an exact kernel version, however.
It really depends. I've seen servers that reboot every 24 hours as well as servers that are constantly up. I would say to reboot every kernel or systemd upgrade