I have S20FE, not S21 Ultra but if the phone is new that's completely normal, in a week your battery will get much better, in two weeks should be even better than it been after the first week. that's the case with samsung phones nowadays.....
sorry for delayed response,ok bare with me I have a few ideas.
1.turn in dark mode 2.put apps you don't use in deep sleep 3.turn off nearby scanning device 4.turn off default print service 5.change network mode to LTE/3g/2g from 5g if you are not in a 5g area 6.do a partition cache wipe
give these a try first and let me know if you have any luck