I noticed the same thing. I tested an iPhone 6s on iOS 14 and compared it to iOS 13. iOS 13 gave me about 4 1/2-5 hours of screen on time with at least an hour of screen off with no issues getting me through a day. After updating to iOS 14, I get 3-3 1/2 hours of screen on time, with 20 mins of screen off.. Definitely a hit in the battery department... I'd give it a few updates, Apple should fix it. Don't forget that it is in fact an early version which comes with issues under that category.

The battery health does not drain every update, it simply re-checks the physical condition of the battery and it happens to be changing because it's doing it's job.