It makes sense that you don’t know much about this stuff as an iOS dev. But it’s reasonable to expect you to have at least basic knowledge of major technologies adjacent to iOS dev. After all, your iOS apps will likely communicate with systems built on these technologies. Certainly it’s necessary to have at least a passing familiarity with them.

Therefore, if you feel weak during the interview when asked about one of these technologies, you should defer to speaking about your experience interacting with it as an iOS dev. For example, speak about a backend API you had to interact with, and how the queries it allowed you to make impacted your iOS architecture. Talk about JSON, relations, indexes, etc. Challenges you faced, problems you discovered, lessons you learned. Make it relevant to both iOS and whatever technology the interviewer is asking about.

It’s never a bad idea to tell a story.