This is exactly what I was going to mention. The severe drain that I had once on XS Max in July 2020 (Apple Music..although I never used it), few times this year with iPhone 12 Pro Max was due to apps running constantly in the back ground.
Mail.app for example ran non stop, Dropbox, Google Drive, also my home alarm system app did this. just draining daily battery life
"Find My..." app was running overnight for me (seemed to run 1min per hour), but no drain.
3rd party apps that seem to just constantly run, I'd delete them...reinstall and it would do the trick.
The Mail App, close it. I did a hard reset...that seemed to solve that problem.
Go to SETTINGS > Battery. Look down to see the chart, see what apps may be running in the background constantly.