Creating a cross-platform mobile app in 2021 can be complex due to performance, cost-effectiveness, and scalability considerations. However, frameworks like Flutter, Ionic, and React Native offer solutions to these challenges. Flutter is a free and open-source framework developed by Google that allows developers to create native mobile applications using a single code base. It uses the Dart language and provides simplicity, great SDK tools, and constant updates. On the other hand, Ionic is an open-source UI toolkit for building performant cross-platform mobile apps, which use HTML, CSS, and JavaScript, with support for different technologies and great performance for beginners. React Native is a cross-platform framework that uses React components to build unique mobile applications, offering an easy learning curve, great productivity features, and incredible performance close to platform-specific code. When choosing between these frameworks, it's essential to consider the specific needs of your project, such as performance, cost-effectiveness, scalability, and ease of use. Additionally, integrating a headless CMS like Strapi can provide a seamless backend solution for cross-platform mobile apps.