I doubt iOS has a large market share in Iran.

Also, for something like this you don't want a platform that requires you to essentially use the App Store and nothing else.

   Briar is available on Google Play for devices running Android.

10% of devices or less.

Unfortunately, due to safety reasons Apple cannot allow you to leave the walled garden, it is only in your own best interest. All communication services on our iOS devices require at least one US-based NSA-integrated middleman. /s