I had something similar happen when updating to One UI 6. Idle time on battery dropped from 2 weeks to 3 days.
The solution was to wipe system cache from recovery menu (God bless that random indian guy on YT).

I feel like the battery is still drained a bit faster than it did before, but at least idle time battery drain went back to previous state.

Android constantly gets apps stuck at 100% cpu for various reasons, and the battery info stuff is so useless, you'd never find it without htop in termux with root.
I'm quite sure if you just got android to show actual process cpu use, you could easily clear the cache, reinstall, or remove whatever app is causing it in basically every case, within a few minutes.

To be fair debugging standby is a bit different since you can't sit and watch htop as easily, but I've found offending apps will drain screen on or not, so can be identified with screen on.