Your iPhone’s battery is fine. No two batteries are identical in many aspects (date of manufacture, exact chemical formulation, exact charging conditions, exact usage characteristics etc.). Batteries will age slightly differently on a day to day, week to week basis, but on an annual basis the results are usually within 1% or 2% in regard to capacity.
If the battery is aging unusually after one year or two years you’ll need to look at your usage patterns, charging patterns, charging equipment and storage conditions.
Please follow the advice from the manufacturer. The Apple Support article below offers many helpful suggestions for the care and treatment of your iPhone battery.
iPhone Battery and Performance - Apple Support