What appears to be a widespread issue is affecting Galaxy S21 Ultra devices and looks like the camera app is the culprit. In some cases, the battery drain can go as far as 21 percent in seven hours and only 15 minutes of screen time. Sadly, the regular battery stats monitor does not detect anything wrong.
https://www.notebookcheck.net/Samsung-s-Galaxy-S21-Ultra-has-battery-drain-issues.545791.0.html