We play waterpolo."jouons au" is marked incorrect and "faisons du" is correct.
Yet your explanation says to use "jouons au" for a sport that you play regularly. "We play waterpolo" means we play it regularly. That's an unambiguous English sentence. There is no other way to translate that. No English-speaking person would use the phrase "We play" for a single incident. They'd say, "We're playing waterpolo." This seems like a bug to me.
Even the article you link to earlier in this discussion uses "jouons au" for waterpolo. Either you need to explain this better or change the quiz answer.
ETA: In fact, if you type "We play water polo" into Google translate, it says "Nous jouons au water polo." If you google "jouer à vs faire de" you get this explanation:
To remember when to use each verb: if the sport involves a ball, use jouer. If not, use faire.
Someone brought this up 3 years ago. You updated the lesson 2 months ago. This should've been addressed already.