I bought 4 week ago iphone 11 and the battery health is going down 100 to 97 whats the problem

Hi,

This should help you to understand how is battery health working, how to maximize battery life and detect if there’s any problem with your battery.

Is your iOS up to date? (currently 14.5.1)

About recalibration of battery health reporting in iOS 14.5 - Apple Support

There is no problem. Normal battery function. When it gets to 80% or less, get it replaced.