It is not possible to build a normal app that runs on both platforms including iPhone and android app at the same time. Fortunately, some companies have web-based technology to build iPhone and android app at the same time. These web-based technologies help to attain native react progressive web applications that build apps to run all platforms. It is also a rumor that iOS will start support to Kotlin soon, and it will be the best platform to build apps on both android and iOS platforms. Until and unless the best option is based on progressive web programming. What do you think about it?