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.

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.

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

You're welcome.