What is the difference between גבר and איש ?
in my Hebrew classes at the university I learned "איש" as man but Duolingo teaches "גבר " as man.
Israeli here. While איש is still male, it is in fact more gender neutral, kinda like "person" or "human". גבר is more gendered. When someone says "be tough, be a man", it would be translated to "תהיה קשוח תהיה גבר". When someone says "be a good man", it would be translated to "תהיה איש טוב" or "תהיה בן אדם טוב"
Note: I did here the mistake of translating imperative "be" into תהיה and not into היה. This is a common Israeli mistake that's become half idiomatic already, using second person future as imperative instead of imperative.
I dont know why we all do it, but I suspect the reason is because imperative sounds more rude and in writing it looks exactly like passive participle (but sounds differently, i.e. Ktuv and Ktov are both כתוב)