Part of the issue when evaluating frameworks is expectations and not understand the plusses/minuses. If you are looking for a framework that will do 1 codebase for all logic and UI, without sacrificing any UX or capabilities, you'll probably be let down. Kotlin Multiplatform will be great for sharing logic and architecture. UI is somewhat of a different case. Why Xamarin wasn't great here is you need to do EVERYTHING in Xamarin, and write custom bridge code when not. It's an entirely different world, which bad IDE support for most of it's history. Jetbrains makes excellent tools, and if you understand that the UI will be "native", then there's a lot of efficiencies you can leverage here. If you get frustrated because you can't make one thing do all things, then yeah, it'll let you down.
Anyway, yeah, they're different.
Yet both Android and iOS allow embedding a Javascript engine in an native application with no effort whatsoever.
Well like it or not JS is first class on both platforms as they both have a JS engine at the developer's disposal, Kotlin or C# aren't.
If it was first class, there would be official Android APIs for JavaScript, debugging support on Android Studio, project templates on Android Studio.
Instead it is a web widget with its own little island of HTML 5/CSS 3, hardly first class.
The support is not much different than getting chromium and compiling it with the NDK.
The only mobile platforms where JavaScript is first class, alongside the other platform languages is on ChromeOS and UWP.
A language is first class when the complete SDK stack tooling has support for it.
IDE, debugger, docs, project templates, profiler, OS APIs.
That's not what first class means to you. You can't just make up the definition you want just because it's convenient for your. First class means it runs on the platform without any form of external or third party runtime.
Hey, by your definition even web pages are first class on mobile devices, as they don't require any form of external or third party runtime, maybe we can even call them native apps!
If JavaScript doesn't require any form of external or third party runtime, then why does React Native bundle JavaScriptCore?!?
In a nutshell this has the same limitation has Xamarin.
The Business Logic is shared , but the UI Logic and the Technical Logic aren't shared or not completely.
The Xamarin community has been struggling with this issue for half a decade and they ended up re-writting their own rendering engine[0] (similar to Flutter) in C# on top of Xamarin to obtain truly MVVM Cross-Platform Framework.
My point here is very simple , getting Kotlin to run on iOS is great, but it's somewhat a waste of time because of how much time and effort it would talk to create a Runtime or Rendering Engine to normalize UI/UX on differents platforms.
[0]https://github.com/AvaloniaUI/Avalonia