Fantastic glad to find this forum to discuss about s21.
How are you s21 users.
Well i am new s21 ultra 5G user just bought 2 weeks ago.
Sadly saying after 6 years switching from android 6 to android 11
Galaxy note4 to S21 ultra 5g
After 2 week of use i still have doubt whether this worth for the price or not. battery 5000 yet to avoid draining we had to disable all shit.
Currently my setting are
1. Set to dark mode
2. Disabled bluetooth
3. system sound and vibration turned OFF
4. 5G & 4G turned OFF, running on 3G
5. Nearby device scanning turned OFF
6. Turn on wifi automatically feature OFF
7. Detect suspicious network turned OFF
8. Display adaptive brightness turned ON
9. Motion smoothness in standard
10. Screen mode set to natural
11. Screen resolution FHD+
12. Always on display turned ON with tap to show for 10 seconds
13. Location ONYet i would not say it is impressive battery. Whats the point of having highend phone yet hav to adjust eventually.
Never streaming never browsing just playing with setting can drain the battery fast.
Some claims its happening due to recent update. I do not know.

I know the feeling with my Note 20. The standby of the newer Samsung is twice as bad as the old Samsung.
I suggest you try Bixby Routine. Since your Location is ON 24/7, then you can set one whereby every time you left a location, the WiFi will automatically be turned off. And automatically turned ON when you enter a certain location. And you can set other Bixby Routine for other functions as well.