After a long time of users asking, Valve has actually added an official Battery Charge Limit setting in the latest Steam Deck Beta update so you no longer need to use third-party tools.
Almost no modern device does a traditional S1-3 sleep. They all do S0 standby/modern standby in windows 8+ parlance. The system is on the entire time. So “waking up” to go to hibernate is basically the same as doing it from a normal on state.
That’s basically what hibernate is. Shouldn’t be hard to offer as an option.
The difficult bit is having it wake from sleep to hibernate itself. I suspect that would require hardware.
Almost no modern device does a traditional S1-3 sleep. They all do S0 standby/modern standby in windows 8+ parlance. The system is on the entire time. So “waking up” to go to hibernate is basically the same as doing it from a normal on state.