I have a Samsung S20FE (Android 11 + OneUI 3.1).
I was learning about the different battery optimization settings. I think I have a good understanding of Android's Doze mode.
Now, I've seen there is (under Battery → Background usage limits) something called "Deep Sleep".
According to this question, it seems "Deep Sleep" is OEM specific, and is not found in every manufacturer's device.
I noticed that an application that is already excluded from "Doze mode" (in other words, an application that is NOT optimized) can not be excluded from "deep sleep mode" (in other words, can not be added to the never-sleeping-apps list).
Thus, I suppose an application goes first into "doze mode", and then into "deep sleep". Am I correct ?
If yes, under what circumstances does an app go into Deep Sleep ? Could an app like Skype (that is natively allowed to wake up the phone even in Doze Mode, I believe) go into Deep Sleep if it isn't used for a while ? Does it make sense to add Skype to Deep Sleep's never-sleeping-apps list if I want it to be always responsive (i.e., I want to receive Skype calls even if I haven't used Skype for some time) ? Or is it unnecessary ?