The problem is that Duolingo optimises for time spent on the app, not for progress in the language. The majority of experienced language learners do not recommend it.

I found this to be a good follow up to "“the book", ideal for anyone who has learned some of the basics of Rust and needs to consolidate their knowledge. I find "typing along" to examples is a great way to learn, and the included projects are a lot of fun. Plenty of additional practical information about systems programming too if you are new to that as well.