What are you starting out on? Kotlin has more web presence, but is pretty much Android-only on the mobile app side. Flutter is theoretically crossplatform with relatively low serverside mindshare.
I think kotlin is mostly used for android development and is a programming language. Flutter is mostly with cross platform development. It uses dart as programing language which is very easy and fast to learn.
This is hands down the best book I read about node. As long as you're already comfortable with JS, this should be more than enough to have you write your own Node apps. Best thing about it: it doesn't limit your to writing node servers like most other intro books. You start seeing node as JS removed away from the browser to a standalone language and not just a way to write javascript web servers.
When I went through it, it was all in es5. So, like I said, if you're comfortable with JS - this shouldn't be a turn-off
