avif has been fully supported in iOS since version 16.4. So the failure is on the app developer for not including it. Often with closed projects like these it’s caused by multiple teams not communicating.
https://caniuse.com/?search=avif
Android is more tricky to define as the app developer is free to use any library they want. But officially it’s been supported since Android 14.
https://developer.android.com/media/platform/supported-formats










I know I’m in for a rough time if they open up with the London system.