All batteries, not just those in the iPhones, will degrade over time. Apple does not consider that an iPhone's battery requires replacement unless it cannot maintain, at least, an 80% charge after 500 full recharging cycles. There is, most likely, nothing wrong with your phone's battery. However, if you feel differently, I suggest that you take it to your local Apple Store or Apple Authorized Service Provider to have them take a look. Alternately, you can contact Apple Support directly by simply selecting the "Get Support" link in the upper right-hand side of this forum's web page. However, don't be surprised if they tell you the same thing as I just did.
Ref: About the battery and performance of iPhone 11 and later - Apple Support