If you're familiar with Jetpack Compose then Compose for Web should be familiar:
https://compose-web.ui.pages.jetbrains.team/
disclaimer: I'm judging from marketing material here: Compose for Web allows you to build reactive user interfaces for the web in Kotlin, using the concepts and APIs of Jetpack Compose to express the state, behavior, and logic of your application.
Not sure how mature it is, I only use Kotlin for server-side stuff.