The only useful place for learning anything is from reading the forums for each exercise. Naturally Duolingo has since shut down the forums thus removing one of the only really useful outlets for asking questions and getting clarification on things.
Perhaps the worst thing of all though is the huge reliance on idioms. There are translations which are entirely idiomatic and have little do to with what’s actually on screen. I find this to be actively sabotaging to learning because you’re not actually learning what’s being said, you’re just being taught that “X means something like Y” even though none of the words or grammar really lines up.
I could go on and on about the low quality of the Japanese lessons. It doesn’t seem like other languages are quite this bad on Duolingo but it definitely makes me think twice about renewing my membership.