SE. How long is a day for you and what are you doing on it? Mine lasts at least 8 hours with light use (mostly standby with an hour of music but no streaming) before I decide to charge it around 50%, which is about what I'd expect of my phone 5 years ago.
Are you using cellular exclusively during those 8 hours? "Apple Watch Series 6 (GPS + Cellular) usage includes a total of 4 hours of LTE connection" according to Apple. (https://www.apple.com/watch/battery/).
My LTE only usage includes about 30 minutes of streaming and the rest just glancing. I can't get through a day like this.