why i cant see my battery health

If you have had your battery replaced with a new one that is not a genuine Apple battery, you will not be able to see Battery Health.

You can find more information here:

About genuine iPhone batteries - Apple Support

Parts and service history

With iOS 15.2 and later and iPhone XR, iPhone XS models, and later—including iPhone SE (2nd and 3rd generation)—you can go to Settings > General > About for the parts and service history of your iPhone. You can also find out if the battery has been replaced. If the replacement was done using genuine Apple parts and processes, "Genuine Apple Part" will appear next to Battery.