The battery seems to drain quickly for me too. My previous Samsung Galaxy S7 (4.5 years old) has a longer battery life than this one. Otherwise, I am very satisfied with it.

My battery lasts much better - I have between 20-40% remaining battery at the end of the day.

These poor battery runtimes are because of the Exynos processor. You have to make sure that you buy the Snapdragon variant.

Since I switched off VoLTE, the power consumption in standby has almost halved. Currently, my S21 loses about 3-4% overnight (no 5G, VoLTE switched off, only WLAN active).

My battery discharges 30% overnight in standby in normal use and in power saving mode the battery lasts just 8h 😀

It could be a defect or there is always a certain series variation in the quality of the SOC. Other causes could be, for example, poor reception, especially 5G is very dependent on the transmission mast, so if your device is constantly trying to connect with high power, this can also pull on the battery. In any case, it is not "normal", you should easily get through the day with a few hours of "on screen time".