How to ensure backward compatibility when releasing a new version of a mobile app?

Backward compatibility when releasing a new version of a mobile application is achieved through several methods:

• API Versioning: The server must support older API versions so that old clients can function correctly.
• Feature Flags: New features are enabled via feature flags to control their activation.
• Data Migration: When changing data structures, support for the old format or migration with maintained compatibility should be ensured.
• Graceful Rollback: The ability to quickly revert an update if issues arise.
• Testing on Different Versions: Checking the application's operation with various server and client code versions.
• Handling Deprecated Functions: Old functions are not immediately removed but marked as deprecated and supported for some time.

For example, if the application uses an API to fetch data, the server should handle requests from older versions so that users who haven't updated do not lose functionality.