Gradle + Kotlin: Problems with subprojects and plugins

Gradle 6.1.1
Link on stackoverflow: https://stackoverflow.com/questions/60142502/gradle-kotlin-problems-with-subprojects-and-plugins

I have been trying to convert my projects’ gradle files using Kotlin DSL but so far failed. All my projects are multi-project builds in Java.
I followed the plugin subproject examples here

It looks like that:

plugins {
	idea
}

subprojects {
    apply(plugin = "java")
    
    dependencies {
       implementation("com.google.guava:guava:28.1-jre")
       //...
    }
}

The java plugin does not seem to be understood in the subprojects and all the ‘implementation’ lines get an unresolved reference.