Recently bought S21+ and I'm disappointed by the standby battery back up. Mine is exynos variant. It's discharging significantly when not in use also. Dono what can be done. The following pic of today usage. I used the phome very mildly mostly beinh in standby only.
This differs if u use wifi google service take less battery. Same way if u use mobile data google service battery usage go high.. clearly can make u used wifi most of the time
Check if all your accounts are synced properly and has no login issues. Next, clear the cache and force restart Google play services under the Apps. Your SOT will surely see an improvement.
If your device is new give it atleast 5 to 6 days to learn your usage patterns. Also turn off 120hz and set screen mode to natural if it's on vivid, it will save a lot of battery. If this works then mark it as solution.
It may not be the only cause. But Chrome consumption of 13.6% that too just running in backgroud is really bad. Disable chrome and use Samsung browser. Set your apps to sleep when not in use too.