Any s21 uses noticed overnight battery drain? At 10pm last night the battery was at 38%, and at 6.30am it was at 5%. There was no wifi or mobile Internet connection and its not been used so it is weird. This is twice I've noticed this, but if it's at 70% or higher I don't think it drains as much.
I've experienced the battery draining quickly over the past few days. Upon googling it, apparently it's a known issue to Samsung that occurred as a result of the latest February security software update. Hopefully it's quickly resolved!
So I've just been reading elsewhere, and it mentioned there was a patch that was going to be released and it would be in the coming days (article was a few days ago). I did a manual software update search and it's already available and have just downloaded and installed it. Fingers crossed that solves it! Suggest you do the same 🙂
Always look at App permissions as well in these types of scenarios, as some apps might be able to turn on WiFi, location etc as they please. Try airplane mode if you must at night and see if same thing happens. Alternatively like me just keep phone on charger so you wake up to 100% battery.