If I buy an iPhone in France will it work in the USA?

It will certainly “work” although it might not have access to all of the frequency bands currently in-use by U.S. carriers.

DO make sure that it is NOT “Carrier Locked”

You’re welvome.

Best of luck.

DO highly recommend that you purchase directly from “Apple” - and pay “full list price” - to ensure that you get an unlocked phone.