One of the primary challenges in mobile app development is ensuring compatibility across different devices and operating systems. Developers must account for various screen sizes, hardware capabilities, and software versions. This requires thorough testing and optimization to ensure that the app performs well on all intended devices. Moreover, developers need to stay updated with the latest advancements and updates in the operating systems to ensure their apps remain compatible and secure. The use of cross-platform development tools, like React Native and Flutter, has become popular as they allow developers to write code once and deploy it across multiple platforms, saving time and resources.