Seperate kanji lessons
I think there should be a section (or multiple) that only focuses on teaching you the 2000~ basic kanji/kanji vocab words (readings, meaning etc.). I know the current system already teaches you some but for a lot of words it doesn't and it also doesn't provide enough of them in my opinion.
It would be nice if DuoLingo re-vamped the way it handles kanji in the course, but I think it is beyond the current scope of the program. DuoLingo was not developed to teach languages like Japanese, so it doesn't really have a good way to deal with kanji. The course collaborators must work within the limitations of the program. Many of these issues are unique to Japanese, due to its complex writing system. It might be a while before they are resolved.
At the moment, it is best to seek out other resources to study kanji (and grammar) in addition to what is offered by DuoLingo. There are many quality programs and websites to choose from. I highly recommend the app, LingoDeer, for anyone who is new to the language. It does a great job of introducing Japanese sentence structure and building a solid foundation for further learning. For kanji, I like the app Kanji Tree and the website WaniKani.
I also would like to see an improvement in the way kanji is handled. Lately I seem to be getting questions that require kanji that hasn’t been introduced yet so it’s a matter of guessing or peaking at the answer. It’s very frustrating and has certainly slowed down my learning.