That's far from being accurate. You will not be able to share any code between the platforms as the code will be based on the native APIs which are completely different.
There’s a distinction between developing for iOS and Android with Kotlin and sharing code, no doubt. Kotlin definitely targets iOS and Android but indeed you cannot share 100% of the code, far from it. With Kotlin 1.12+ you certainly can share code, but the developer has to know a lot about the platform specificities.
However, more and more Kotlin libraries are developed as seamlessly multiplatform to deal with HTTP, serialization and coroutines. Also, an extensive standard library is available on all platforms. No doubt the code sharing facilities will grow with each release. Kotlin 1.4 coming out soon will certainly enhance this aspect.
If one would like to learn about Kotlin code sharing, you can read this interesting article:
Kotlin Code Sharing . Notice how easy it is to target the correct platform by using a couple of keywords: expect/actual, though you have to know about the platform itself.
If you really want to share 100% of the code between iOS and Android then Google’s Flutter framework is excellent for RAD development. It’s even more popular than Kotlin and once you understand the widget concept (everything is a widget), it’s easy enough to build great interfaces. The only drawback from my point of view is that one will have to learn Google’s Dart language which is not as easy and modern as Kotlin.
From my point of view, the perfect combination would be Flutter/Kotlin, but I doubt it’ll happen.
There are other eco-systems that allow you to develop cross-platform applications, so it's good to have the choice.
Anyway, I hope it was transparent, I did not mean to disparage B4X, though I believe it has shortcomings. B4X certainly has its place and some developers do make a living out of it.