@sendpaws
KDE has the same thing. Even worse in a way, cause if I enable suspend-then-hibernate via KDE, it does work when the timers run out. After say 5 minutes the system goes to sleep, and after an hour it hibernates. BUT if I make the mistake of putting the system to sleep via the start menu option, it NEVER hibernates, even if you expect if to.
As far as the user is concerned, sleep is sleep, and I did tell it to hibernate after sleep... But no. Turns out the start menu option remains tied to systemd suspend.
@alyx it worked on mate finally after running a script on a forum and then setting that option up in the systemd sleep config.
https://forums.linuxmint.com/viewtopic.php?t=425394