Kotlin is a language like any other. It does not have any specific technology binding and is capable of executing anything. It is an exception to any language that has limitations on use.
Of course, the support for extra libraries and tools always varies from language to language. Kotlin can be used as a web backend without any hassle, but there is not as good a support as other solutions, even by having a small community today. But almost everything that is good for Java is for it to a greater or lesser degree, so the support is not that small.
Angular is a frontend technology . Support in browsers for languages other than JavaScript is recent. Kotlin even has a JavaScript generation mode, but when it can generate its own code it will be more powerful. In any case it is possible to integrate with Angular, but it will make little sense, and will have little compatibility. It will be more interesting to have a framework of it to replace the Angular in the browser. But of course, if it is used in , it can communicate seamlessly with the client running Angular, it's completely different things that communicate through universal protocols.