I'm using Java 11 and Java 17 with Kotlin without issues. When targeting Java 8, Kotlin creates helper classes for the default methods on interfaces as that is

I'm using Java 11 and Java 17 with Kotlin without issues. When targeting Java 8, Kotlin creates helper classes for the default methods on interfaces as that is not supported in Java 8, whereas on Java 9+ it uses Java default functions. However, you can target multiple Java versions, as I've done that with my projects for 11/17 support.