You can carefully tap a region on the graph to see which app is doing the most draining. Messenger apps tend to do strange things and apps that like to check-in too as well as location & background refresh apps.
About once a month, if I think of it or if my iPhone SE (1Gen) acts too weird, turn everything off. and do a hard restart. (Don’t make this too much of a habit; just a last resort.)
Settings / App Store / Video Autoplay Off seems to have fixed it. Both phones had it turned on by default - creepy! The drain with it turned off is about the same as when wifi is turned off.
How did people discover this obscure “trick”?
All I can say is that when I saw the App Store was using so much battery I went into settings to see if there was some way to make it use less battery, and I noticed that setting. I hardly ever use the App Store - I go into it every day or two to update apps, and maybe once a month look for a new app for some reason (it’s probably less often now,) I never want video autoplay ever anyway - I want videos to start when I activate them - so I was glad to see that changing that one thing fixed the App Store battery issue for me and turned off videos as well.
Interesting…my two year old iPhone 11 (not Pro) has 85% Max capacity?
Rich
The battery drain problem is back! As predicted, my battery health has not dropped below the 80% apparently needed for Apple to fix it under warranty (expires any day now).
I recently installed an app that connects to a camping device (ironically a smart 50Ah battery) by bluetooth and that could be the culprit, although it doesn’t show up as a high devourer in the battery settings of the iPhone. Also installed a Dlink app for setting up a wifi network.
I have force-quit both of them to see how my phone goes tomorrow.
Now running iOS 15.1.1
Ok - I have replaced my iphone 8 with an iPhone SE (acknowledging that the SE is about to be updated!). The transfer was seamless - it even prompted to update to 15.3.1.
The battery drain issue is back! 
Video Autoplay was off in Settings. The bizarre thing is that the Home app is consuming 32% of the battery energy even though I rarely use it on the iPhone and, of course, the iPhone does not act as a Home Hub (maybe I should check if that has quietly changed?).
Another possibility is that I have selected iCloud Backup for the new phone (but disengaged it after first backup as I prefer local backups - Mojave/iTunes). I don’t see why a non-functioning iCloud backup would affect battery life.
A new phone, or a phone recently restored from backup, or a phone reset and rebuilt from scratch, can take a few days to do some background processes that can use more battery than usual. Give it a few days to settle down. It may be that you still have an issue, but battery usage may settle down a bit, too. Also, as I recall the battery report isn’t always useful during this period.