Hi, @abid4566. I am very confident that you can get significantly more battery life out of your phone than what you have reported.
It's strange that your phone is overheating, and this would unquestionably be contributing to your battery draining more quickly than expected. I suspect that the two issues are not mutually exclusive.
I'd definitely suggest starting your phone in Safe Mode to see if a third-party app is perhaps causing these issues:
If the overheating is not evident whilst in Safe Mode, then it suggests that the trouble is being caused by a third-party app. To resolve this, just exit Safe Mode, then begin uninstalling apps you've downloaded one by one (restarting the phone between each app uninstallation) until the issue fixes itself. Once you've identified the troublesome app, you can reinstall the other apps via the Galaxy/Google Play Store.
In addition to what @Glenntech has asked about your battery usage, I'd recommend consulting the guide below:
Furthermore, the guide below (from Samsung US) has some very helpful tips about putting unused apps to sleep. This can dramatically increase the battery life you are getting from your S21 Series phone:
https://www.samsung.com/us/support/answer/ANS00088422/
Combining all of these steps is likely to noticeably improve the battery life that you have been getting.
Please let us know how you get on.
