Commenting out the toolchain completely then results in a different problem:

* What went wrong:
Could not determine the dependencies of task ':kotlinNpmInstall'.
> Could not create task ':rootPackageJson'.
   > Could not create task ':client:web:browserTest'.
      > 'org.jetbrains.kotlin.gradle.targets.js.webpack.KotlinWebpackCssSupport org.jetbrains.kotlin.gradle.targets.js.webpack.KotlinWebpackConfig.getCssSupport()'

I just encountered the same error when trying to use BuildKonfig. I am not sure what version of the Kotlin Gradle plugin I’m using as it’s transitively included but it is probably 1.8.20 which should be recent enough. If I attempt to explicitly include it by running

plugins {
 id("org.jetbrains.kotlin.plugin.scripting") version "1.8.22"
}

the compiler complains that

The request for this plugin could not be satisfied because the plugin is already on the classpath with an unknown version, so compatibility cannot be checked

edit; I was able to overcome the error once I changed the plugin version to

1.8.21

matching BuildKonfig 0.13.3:

buildscript {
    dependencies {
        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.8.21")
    }
}
plugins {
    id("com.codingfeline.buildkonfig") version "0.13.3"
}

@rocketraman can you upgrade to 5.6.2 which uses 1.8.10?

Still can't get it to work properly and run all my tests, but that's another issue: https://kotlinlang.slack.com/archives/CT0G9SD7Z/p1692941161344089