You will run into mountains of issues with USA systems if you insist on using the è. You will fill out physical paperwork at the hospital. How will it be translated by the typists and OCR? Passport matching against the airline information. Will it match? School enrollment: will all the username systems be ready for the UTF-8 character?

Even big carriers with automated workflows get this wrong, e.g. put "Rémi" in your Amazon address, get a confused UPS driver looking at a "Rémi" label.

Relevant XKCD:

https://xkcd.com/327

It's not allowed in most US states. If you already have a name with an accent most companies and agencies will just remove it.

Most states won't even allow you to give you child a name with a diacritical mark.