If a Muslim asks you "Given that Muhammad was illiterate, how could he have known X, Y, and Z? Isn't this a miracle?"
And if you directly answer the question (how could he have known), you are effectively telling them that this question and its answer is consequential to the question of whether or not Islam is from god.
If you do that, then you're just swimming with them in the ocean of evidence about Islam.
Don't swim with them. Instead, tell them the question is not consequential to the question of whether or not Islam is from god. And if you want, ask them to explain why they believe its consequential, so that if you're convinced, then you could care about this question like they do.
Don't answer inconsequential questions.
Don't swim in the ocean of evidence.
Narrow down the discussion to one main point, one crux, one bottleneck. Example: "Why does this supposed miracle matter, given that Islam claims perfection while having imperfections? Does the miracle somehow convince us that all the imperfections we see aren't really imperfections? How exactly? Please explain your view."
