I bought my iphone 7 plus 3 months ago and its battery Health is 95%

Any number of things can change battery health. iOS updates, heavy usage, etc. If you turned the phone off and left it off for a day, the next time check battery health, the number would likely be higher. It's not really something you should get worked up over unless the battery is less than 80% in the first year.

That's what batteries do. They lose storage every minute.

You're welcome.

Battery Health is not finite and changes as the phone is used at different times and situations. Apple doesn't consider a battery to have an issue unless Battery Health goes below 80% in the first year of use. I would not worry at this point.