Battery maximum capacity 99%

No, it is normal for max capacity to reduce. Rate will varey depending on how much you use the battery. There is also likely to be some early life reduction.

It is assumed to be OK until around 80%. Sometime around then the phone will tell you it needs a battery service.

This happened to me also when I got a new iPhone two years ago. It dropped one percent of the original capacity after about a month too, but right now it is at 97%. I do not think that you have anything to worry about.

As batteries age, they gradually loose their maximum capacity, this is normal.

Maybe your phone was used you should go to the store to tell them the problem

But in 1month of use it can’t be possible

One percent from perfect.

Ignore it for a few years.

It is possible, I have had this exact experience, and know other people who have had this happen. There is nothing to worry about.