Creating assets like Capes that can be attached to any character and still look great on a single platform is a complex problem. Combining that with a wide range of platforms that games like Fortnite support greatly increases the complexity.
For tutorials about Cloth Simulation in UE, check out the tutorials available here: https://dev.epicgames.com/community/learning?type=tutorial&product=5_unreal_engine&category=character-and-animation