I'd pick it over Swift if targeting Android since it can build and run in the JVM as well as natively -- and has Swift/ObjC interop. Its also very usable on the server if you wanted to, since you can use it in place of Java and tap into the very mature JVM ecosystem. If that's what you're into.
And I have a lot more faith in JetBrains being good stewards of the language rather than Apple, who have a weird collection of priorities.
I tried to use Vapor with Swift recently and struggled to get something working because the documentation looked comprehensive, but had a lot of gaps. I ended up throwing it out because I didn't have the time to dig through the source to understand how to do something, when I could use a mature framework in any other language instead.
The promise is there but I'm just not ready to invest. My youthful days of unbounded curiosity are coming to an end and these days I just want to get something done without much faff.
However, the Kotlin community is fundamentally all about open source, whereas Apple & iOS Devs have an allergy to it. The quality and quantity is already miles above the vast majority of what's in the Swift ecosystem. https://klibs.io has all the native compatible libs. And if you're targeting a platform where the JVM is available then yeah, it's massive. Compose makes UI tolerable compared to JWT too. Even large projects like Spring are Kotlin first nowadays.