Well there is kotlin-native which allows you to write kotlin libraries that compile to IOS and Android. Which you can than link to objective C or flutter based UIs. Or even react native. That allows you to share a lot of code between different platforms. A growing number of Kotlin libraries are multi platform meaning you can use them on IOS, the JVM, and in browsers.
Java doesn't have that and it's kind of an increasingly dead language for mobile development. Some older android projects still use it. But Meta is late to the game of migrating away from it. Many companies did that years ago and the vast majority of new Android applications is using either Kotlin or Flutter/Dart.
I have good hopes for Jetbrains extending the jetpack compose/compose desktop/compose web ecosystem to IOS at some point as well. That would create some interesting possibilities in terms of targeting just about any platform with kotlin from a single code base. It's a logical next move for them and they've been laying the groundwork with their multi platform compiler strategy for a while now.
Java doesn't have that and it's kind of an increasingly dead language for mobile development. Some older android projects still use it. But Meta is late to the game of migrating away from it. Many companies did that years ago and the vast majority of new Android applications is using either Kotlin or Flutter/Dart.
I have good hopes for Jetbrains extending the jetpack compose/compose desktop/compose web ecosystem to IOS at some point as well. That would create some interesting possibilities in terms of targeting just about any platform with kotlin from a single code base. It's a logical next move for them and they've been laying the groundwork with their multi platform compiler strategy for a while now.