IMO, "learning it" simply means learning how to code in Kotlin and how to efficiently use the Multiplatform tooling. That's the foundation. You can then decide if you also want to apply it to the JS world, which include both website design, or libraries implementation.
In the current market you'll definitely find more opportunities with well known frameworks like React, Vue, or Angular. K/JS will get its own place at some point, once the ecosystem of frameworks and libraries is sufficiently mature.
However, you can definitely complement the use of mature frameworks with K/JS. I do just that.