I feel you could put an emphasis that those are two very different approaches to multiplatform.
Flutter/ReactNative/UnrealEngine is a top-down approach. Some big company (Facebook/Google) provides you a game engine on which you can run your app that run everywhere the game engine run, with the limitations of the game engine.
Kotlin Multiplatform and j2objc on the other hand have a bottom up approach. Each company defines what can and should be multiplatform in their project. The UX stays native. Below the UX, each team defines what makes sense for them to share on all platforms.
Because those are two very different approaches, they will make sense in different use cases.