I should have search more efficiently before asking.
Rapidly came across this article from The Mac Observer. The author explains the option has been removed by Apple :
Until recently, setting your Mac on a shutdown or reboot schedule was easy. You just needed to go into the Energy Saver panel in System Preferences, and use the graphical interface to set up that schedule. Strangely enough, Apple doesn’t include that same functionality in macOS Ventura.
See also DssW's Missing Energy Saver Schedule in macOS 13.
I can't find any mention of removal in the macOS 13.0 release note.
Except the fact GUI is for now removed, this option still is controllable using the pmset
command, that has been often questioned on AskDifferent.
Here is a link to DssW website for documentation or type man pmset
into a terminal to see available options.
For example, the following command would reboot the computer every monday at 2AM.
sudo pmset repeat restart M 02:00:00