From what I heard, the sleep mode on the steam deck is just the default linux sleep mode. It works almost flawlessly.

I don't think it's quite true though because I can leave it in sleep mode for days and it just fires back up where it left off with almost no noticeable battery drain. If I put my desktop pc to sleep (bazzite) it acts like a stroke victim. IF it manages to wake up. Usually it just has to be restarted so I don't waste my time and just shut it down now.