I want this battery health to be good and strong

Battery health is a moving thing.

It is not an error, it is something normally happening with charging cycles, batteries deplete.

Sometimes it can look as if battery health is dropping quick, but after a while it stops and stands still for longer periods of time. If your battery health hits below 80%, your eligible for service and battery replacement, ask your Apple Store about the cost of this

have you read About the battery and performance of iPhone 11 and later - Apple

Support

and maybe iPhone Battery and Performance - Apple Support

and Batteries - Maximizing Performance - Apple

 people report apple does not change the batteries until they are lower than 80% in health