TypeSript is more mature and better option for frontEnd now, but I hope kotlin will catch up.

I wouldn't use kotlin for cross-platform mobile dev. There are few things Android and iOS share, you end up having to codebases in the same language (which it is good in its way). If you want to do truly native apps, just avoid sharing code because you will use different patterns and different libraries and apis. You could share the business logic but that is something I think should be on the server not in the app. The app is only the frontend.