Flutter differs from other cross-platform frameworks like React Native by using its own rendering engine, Skia, which allows for more control over the UI and eliminates reliance on native components. This results in highly consistent and customizable designs across platforms, without needing to compromise on performance or user experience.

Yes, existing apps can be migrated to Flutter. The process involves rewriting the app’s user interface in Flutter while integrating with existing backend services and APIs. Flutter’s ability to work with platform-specific code allows for a phased migration, where parts of the app can be gradually moved to Flutter, leveraging its advantages over time.

Flutter offers several advantages, including a single codebase for multiple platforms, faster development with hot reload, and a rich set of customizable widgets that ensure a consistent user experience. It also provides high performance through its direct compilation to native code, and strong community support with numerous libraries and plugins.

Flutter handles performance by compiling to native code, which reduces the overhead of interpreting code at runtime. Its custom rendering engine allows for smooth and fluid animations and transitions. For scalability, Flutter supports large-scale apps with features like efficient state management solutions and asynchronous programming, ensuring that apps remain responsive and maintain high performance as they grow.