Back when they started, they had a forum where people explained grammar etc which was very helpful. They closed the forum, gods know why.

I read that they’d introduced a subscription tier above Duolingo Super, although I’d never seen it on the web version. Nonetheless, people say that the app explains mistakes in this tier, or at least adds more context. If that’s true, it all makes perfect sense: people wouldn’t pay if the same information was available for free.