battery health

Don't worry about it.

Especially as it's brand new, you have your full warranty term to watch out for other issues:

iPhone Battery and Performance - Apple Support

If you are concerned, contact Apple Support directly:

Contact - Official Apple Support

Anything that causes it to report degraded performance.

If you are concerned, make a note of when your warranty expires (typically one year) and make a calendar appointment to schedule a service visit to your local Apple servicer then.

You can also bring it up if you need to have your phone examined for any other issue.