Exactly this. Services and software are not the same thing, you’re asking for a service recommendation and it can’t be open-source software because it’s not software.

I have never met anyone refer to “screen off” as “sleep”.

https://en.wikipedia.org/wiki/Sleep_mode

The terms everybody else are using are: “sleep” = “suspend to RAM” = “S3” and “hibernation” = “suspend to disk”.

Ok so what do you call “sleep”? You’ve now listed suspending, sleeping, and hibernating as 3 different things.

Suspending to disk usually requires a password on resume.