Hello jh276,
Welcome to Apple Support Communities! We understand that you have some concerns about the battery health of your iPhone. We're happy to provide some information to help with what you're seeing.
Maximum battery capacity measures the device battery capacity relative to when it was new, and is impacted by more than just the passage of time. Batteries will start at 100% when first activated and will have lower capacity as the battery chemically ages. Check out more information here: iPhone Battery and Performance
To help with maximizing your battery lifespan, we'd recommend following the tips here: Maximizing Battery Life and Lifespan
If you're using an iPhone 11, iPhone 11 Pro, or iPhone 11 Pro Max check out the following support article that may help: About recalibration of battery health reporting in iOS 14.5
Regards.