What are your reported Charge Cycles. You should expect on average a 1% drop for every 50 charge cycles. You can certainly set the charge limit to 90%, but the phone will not display an updated Battery Health percentage until after it has been allowed to charge to 100%. This will happen automatically on occasion when there is a charge limit set as long as the device is still plugged in.
For a battery that drains quickly, post a screenshot of what you see at Settings > Battery, and scroll down to view app usage over the last 24 hours. Some apps have been noted for their excessive background processes that consume the battery even when not using the app. Testing is simple by removing those apps and compare the results.
The Meta apps have been the most notable where they had previously acknowledged that an app update had caused the problem. They did follow up with an update that claimed to have fixed it, but you will also see they release about 10 updates per month for bug fixes and sometimes new problems are introduced. In addition, the Google support sites have also been filled with the same battery drain problems seen with some of the Meta apps, so it is not device specific.
As for updating to iOS 18.4.1, yes I would absolutely recommend that update. My recommendation is based more on security than on any changes to the battery usage. It has been recommended by Apple to update to iOS 18.4.1 as it does address 2 major security vulnerabilities.
