I've found Kotlin/Native to be fine, but very basic. It's limited due to lack of ecosystem and minimal stdlib, though this is improving.

There are things you might expect to be able to do trivially (e.g. formatting a timestamp into a date string) had no off-the-shelf approach last time I tried. You'd need to roll your own, or pull in an existing non-kotlin library, e.g. something from C.

I think a lot of issues stem from existing APIs being designed around Java types that will never be available without the JVM.