If anything, I'd say in the US, we almost never use "US" as an adjective. The only cases I can think of are official in nature, i.e. "US citizen" or "US passport", and even then "American citizen" and "American passport" do not sound wrong. However, "US kitchen", "US cuisine", "US car", etc. sounds extremely unnatural, so I'd just always use American.

I don't know if it would work for Duo but it would work in English. In the UK we would be more likely to say "American".