I think it's an issue with the phone and how It determins battery use I can use YouTube chrome and YouTube music with the screen on for an hour each and it only drains 5 percent or so it's only when the phone is idle it drains like crazy
Well I can literally see that I loose 5 percent battery with 5 minutes of basically any app regardless whether it's a heavy app or not and that doesn't show on the battery stats I can tell you that much it's an issue with this phone there's no way a my S10e used to loose 1 or 2 present per hour of Bluetooth music listening and I lose 12-15 present of an hour of the same activity. This phone looses battery quicker than any phone I've had and compared to other phones too. It's clearly a this device issue
I have 2 year old moto g7 play and it's battery capacity is less but gives me double battery backup when compared to s21. Seems issue with either exynos or One UI. I think it's one ui definitely as the Android OS is clean and much optimized to handle any google apps.
But I heard that pixel 4a or 5 battery is also much better than s21 and there are no overnight battery drain issues. 5% battery drain in 8 hours idle for pixel 5. But 12% battery drain in 8 hours idle for s21