In Korean, the subject is often omitted from sentences, so shouldn't "카페에서 무슨 요리 사요?" be accepted as a correct answer?
Yeah. This app sucks with most things in korean. You cant directly translate korean.
In reality Koreans use the word 메뉴 rather than 요리 when referring to a dish.
I really have issues with the Korean sentence order
Why is 음식 not correct here?
To my understanding 음식 is everything with nutrition (including apples) while 요리 is prepared food (dishes)
When do we use 요리 and when do we use 음식?
Does 카페에서 need to be at the start of the sentence or is it also possible to put it behind 요리를
You can place 카페에서 after the topic or after the object. If you place it after the object, you're emphasizing the location of the action rather than the object.