iphone 13 battery drain

Check Settings > Battery and learn what app(s) is/are primarily responsible for the battery drain.

I have found this as well. I have been SO pleased with the battery on my 13 Pro Max, but in the last 2 weeks, I have to charge by the end of the evening. My app usage hasn't changed nor my brightness, so I think it's an issue with the new IOS release.

OK, you chose to ignore my suggestion. But you reached an unsubstantiated, incorrect conclusion.

Good luck.