See this post by msanders916 dated June 12 (in case the link doesn't go to the correct post automagically).
I'm inclined to agree with them.
The TLDR version is this:
First, understand that the software does housekeeping after an update. It can usually be accomplished overnight but that depends on your device and its data. Try to install updates overnight and leave the device on the charger (It’s ok to do so and won’t ruin the battery. That rule applied to older battery technology). This is so that processor intensive tasks like file indexing for Spotlight Search or iCloud syncing can occur then and not during your day.
It's not what iOS 17.6.1 is doing to the battery, it's the update process and not what it updates to. Any update, apparently. That housekeeping happens in the background so the only thing you're aware of is the sudden battery drain for seemingly little no user activity.
I updated my recently purchased refurbed iPhone SE 2nd Gen and (once I got it to successfully restore and update (at least 6 attempts, I thought it was bricked), the battery drain was such that even though I kept it plugged in all day the battery level dropped from 80% to 21%. By the next day it was okay. It probably took less time than for most people because it had only the iOS and not many more than the standard apps on it, very few personal files or media.
So relax, it'll (probably) get better on its own.