Imho, Node.JS is a lot simpler to use.
- It uses JS, which you should already know if you are a web-dev. Kotlin is a new language to learn.
- Node.JS is one executable you can ship. You will literally have portable software. Kotlin needs the JVM, so you will have to install that and lots of updates later on, because that platform is so extensive and central
- NPM has one of the fastest growing module count overall. You will find lots of useful and powerful modules. Keep in mind, that they might also be very bug-riddled and not quite battle-tested
So, for less critical applications, Node.JS is very easy to use over the whole life-circle. If you need to build something mission-critical, you might want to go back to the Java giant and Kotlin.