How long have you owned your iPhone and/or how many cycles does it show in Battery Health? iOS updates don't make batteries lose health. But they can reevaluate the true health of the battery.
On average, you can expect to see a 1% drop in battery health per month of ownership. Or for every 25 cycles you can expect a 1% (on average) loss in Battery Health.
If you've owned your iPhone for at least 8 months or your phone has had 200 cycles, then your battery health is about where it's supposed to be.
There is one constant with battery health and that is it WILL go down. When it reaches 80%, it will then be time to pay Apple to replace the battery.