It pains me, but it turns out this is a feature, not a bug.
https://support.apple.com/en-us/HT207056
• System Customization: Your iPhone will customize system appearance, behaviors, and settings using your current location, for example by
automatically enabling Optimized Battery Charging when you are at home.
I have an iPhone 7 that's afflicted with terrible battery life after installing iOS 14, as documented, commented on, complained and whined about sufficiently elsewhere that I'm not going down that rabbithole today. That said, I read (also elsewhere) that the battery draining is related to optimized charging and that a simple fix is to disable optimized charging and then allow the iPhone to deplete the battery completely before re-charging.
Seemed like a simple fix so I gave it a try. Seemed to work for a day, that's when I found out optimized charging is a zombie feature (i.e.) won't die and eats at your brain.
Hope this helps. Your KPH may vary.
Edit - should have mentioned that my hope is that by turning off system customizations I can also turn off optimized charging and thereby get my battery life back to where it was on iOS 13.