+1 on that. Learning to think in Immutable took a little doing, but once I got the hang of it it wasn't that hard. In some ways, I would even say it enforces good practices.
The other big cognitive shift for me was learning to separate Kotlin from Kotlin JVM. When you're writing Kotlin code on Android you're writing against the JVM, which means you have access to all of the standard JVM libraries - from simple things like String formatting to more sophisticated tools like Retrofit.
When you're in Kotlin Native (i.e., writing for the common module in KMM), all of that is gone, and K/N doesn't have anywhere near as many or as mature support libraries as Java does, because it's so much newer. The language may be familiar, but the environment is very different. Many of the things you have learned to take for granted as an Android developer are no longer there, and you have to either find replacements for them (which means hunting down and evaluating different libraries and learning new APIs), or use
expect/actual
to implement them on each specific platform.