It's a bug with Duolingo. The makers of the course can't fix it, only the programmers of Duolingo. Send them a bug report here: https://support.duolingo.com/hc/en-us/requests/new
Here's an example of a bug report I've sent: https://imgur.com/gallery/JdHZkXK
Yeah the lack of Fuṣḥá endings is annoying me, too. I want to learn formal Arabic first, and then branch out into less formal language.