Hey! Kotlin is on the rise!
I think it's a good choice for backend development.
So, there are some established frameworks on the market like Spring that offer official support for Kotlin now - and that is great. But if you want to bring Kotlin to its full potential Ktor (which is written purely in Kotlin) is the way to go. Despite still being a smaller framework, it is backed by JetBrains and actively under development.
When it comes to choosing a framework... I find that very difficult. There are plenty of resources for Spring as it has been around for two decades and it's hard to kick off the throne. But I personally like to go with a more modern, lightweight framework than Spring. Micronaut and Quarkus are two examples I came across. But there is still little documentation.
JetBrains appears to be investing in the Kotlin backend ecosystem and I expect it to grow in the future.
https://kotlinlang.org/docs/server-overview.html