You need to allow two full weeks - 14 days, but it should have leveled out by now. You should still get at least 24 hours out of it with your current usage. Turning off raise wrist to wake would save a marginal amount more, as the watch tends to wake every time you raise your wrist. Turn off "turn on screen for new notifications". Lower the vibration intensity. lower the screen brightness to the lowest level where you can still comfortably see it. Swipe up to the app drawer and tap the topmost icon for currently open apps. Close them all and see which apps are running in the background - should only be Samsung health and Google digital assistant. You can stop the assistant from running in the background if you don't use it. Just tap the tile and you will get the option. You cannot stop Samsung Health from running in the background (unless you turned the health features off in power saving and have power saving on). Since you are getting 21 hours out of it, you are still getting a full waking day, and you can put the watch on the charger for a bit while you are having dinner or watching TV to give it a boost to give you the extra hours. Even though I get a day and a half, I still charge my watch every morning. There are days when the battery depletes faster than usual, but I boost it in the evening to get me through the sleep tracking and backup at night. I don't go to bed unless the battery is at 40% or more. If you don't track sleep, you can put it on the charger while you sleep and wake up to a fully charged watch.
A factory reset may clear up these issues, but it will start the learning period over again. You may want to attempt to wipe the watch cache before you reset (instructions below). The average up time for a watch with normal usage is 28-36 hours. I get a day and a half out of my watch I do work out, track sleep, use timers and alarms, and Samsung Pay, and everything else the watch was designed to do. I do not use power saving unless my battery goes below 12% (and then it goes on automatically) and I am not near a charger. I keep my screen brightness to about the mid point, have sound off.
