well ... Duolingo sentence is cumbersome to begin with. Anyway, in the typical or usual modern culture now, when it comes to the kitchen and food, cuisine (translated as مطبخ maTbakh, which also means kitchen) usually refers to the domain of various food-related things, like cooking style, food used to cook, spices and all that. The whole food culture. So, if I say "French cuisine" I do mean the French food culture (if I can call it so), and this terminology, is typically translated in Arabic as: مطبخٌ فرنسي (maTbakhun faransiy).
If I'm referring to a specific dish (a meal) which typically French, that would be translated usually as طبقٌ فرنسي (Tabaqun faransiy). And here, طبق (Tabaq) literally means (dish).
Thus, when Duolingo states أكل فرنسي (aklun faransiy) it is a bit cumbersome (and I think even in English, "French food" does sound cumbersome unless maybe the food is made in France?)