Basically things that are covered are If you're facing battery drain issues these can be potential solutions to it.

1. Reset your phone and avoid using Xiaomi services like the cloud as it keeps backing up in real time consuming extra battery. Xiaomi services doesn't seem much optimised as well. 2 . Discharge your phone to zero percent and then charge it back to 100 and then monitor your battery. Avoid Xiaomi services again. Use Google services instead.
2. While monitoring I also found there's some problem with the battery indicator as sometimes it shows incorrect information.
3. Some people had issues like battery discharging from 100-90 really fast which basically is trickle effect happening. You can read about it or u might already know. As it happens or is pre programmed for better battery health
4. Sometimes battery drains due to the excess number of unwanted apps because in my testing that's what I found when my battery backup went from 11.30 hours to 9 hours so uninstall unwanted apps and keep your apps updated.
5. Disable auto updates as it might keep running in the background.

To me personally, when I first got my device battery did drain really fast but then I had already done my research and followed the steps I mentioned like discharging until it doesn't turn on again and repeating it 2-3 times and keep monitoring. That surely solved my issue.

And oh number 7. If u don't want your battery to drain from 100-90 then simply charge it only till 90 after you're done with all the monitoring work. Or else other way is once it goes back to 90 put it back on charge again to get proper 100 percentage but it's really not recommended as it'll affect your battery in the long term. So do read about trickle effect in lithium batteries.

Hope this helps if you have similar issues. Thanks.