The Android app may be developed on Linux, Mac, or Windows using Android Studio. It should be targeted at Android 6.0 and above, and can be built with Java and Kotlin.
Kotlin is preferred for developing the Android app. As a JVM-oriented language, it is fully compatible with Java, and offers more flexible syntax and powerful features. Back in 2017, Google announced that it would support Kotlin on Android as a first-class language. With experience in Java development, you can easily get started with Kotlin.