Mock 3 — whiteboard, 30 minutes. Draw what happens between a user tapping a button and the screen changing: the state change, which views are re-evaluated, how SwiftUI compares the old and new descriptions, and what is redrawn. Then answer: what would make this slow, and how would you find out?
Review. Go back through every interview problem you have not marked as solved, and every flash card you got wrong. Those are the things to study before a real interview.