I moved from France to the USA and can't download apps in the US?

Change your Apple ID country or region - Apple Support

See the above link...

If you can't complete any of the steps, can't change your country or region, or you have less store credit than the cost of a single item, contact Apple Support.

Why not? What happens when you try to download apps? What is the message you receive?

First, were you successful in changing your region from France to the US? Do you have a payment method from a bank in the US and a US address?