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.
I just do it whenever my package manager says to do it after the monthly sudo apt upgrade. Which is most months, but sometimes it doesn't, so I don't.
Ten minutes of downtime a month isn't a big deal.