why my phone battery health coming meximum 98

Because every time you charge your iPhone battery, Battery Health will decline little by little. It's what batteries do. ALL BATTERIES. A decline of 1 - 2% per month is expected and normal. When battery health declines to 80%, it will be time to have the battery replaced. Until then, stop worrying about something which is normal.

Don’t let yourself worry about it. That is very normal. once it gets just above 80%, then it’s time to do something about it.