Good afternoon, there may be a lot of apps running in the background that's draining your batterylife there so quickly, if you back out of that sub menu and go back into "battery"> you'll want to go into "background usage limits"> at the top, there should be a toggle that says "put unused apps to sleep" this will limit apps in the background that you're not currently using and put them to sleep until you use them. This should help with your batterylife
This is a common reported issue on the forum by a lot of users. It's not necessarily a defect. The Phone's AI will provide batterylife to the apps that need it which is why you have to monitor what app is doing what in the background because those will pull the most Batterylife
That's pretty much it as far as your battery goes. If it persists then I would look into if it's an issue with the Battery itself. Monitor how apps are behaving on your phone over time.
Many users of the s21 had this problem but after several updates the problem got better. You need to give your phone time to learn how you use it and it will eventually get much better at conserving power. I had the same problem when I got my s21 but after about 2 weeks, the problem went away once the phone learned my usage patterns.
Little update: I still got the doubt but probably it's because I'm getting anxious, this is the situation for now. The phone can predict my usage, but still, have to charge it to make it through the day
(I turned the phone off the several hours)