Salut VitN !
Thank you for your question!
Since the word for "state," état, has an acute accent on the E, the country name États-Unis needs this accent as well. However, you may well see this name written without the accent, as Etats-Unis, and this is not necessarily incorrect. This is because some French style guides (particularly those of many large, France-based newspapers and magazines) state that accents shouldn't appear on capital letters. It is also particularly common to see unaccented capital letters in France because the French AZERTY keyboard makes it difficult to type accents on capitals. In places like Quebec, on the other hand, it is the norm to put accents on capital letters.
In our course, we generally go by the rule that the accents should appear on capital letters to make things as clear as possible for our learners. I will pass this lesson on to the French team to make sure that the accents appear consistently on the country name États-Unis.
Our apologies for the confusion this has caused! Thank you for pointing this inconsistency out to us.
À la prochaine,