If they bring up graphql, I expect them to say something like "none of the advantages of graphql are applicable in this case, so it may make sense to use if it's already well supported. All else being equal it's probably not a good fit"

The key is that the response should reflect the actual design we're discussing, it should be more specific than something that could be said in any interview.

In an interview it is a negative to not know something. It's a bigger negative to not know something and try to hide that, or to be ignorant of the ignorance. "I don't know" is a fine answer in an interview. "I don't know, here's where I would look" is better