also the build.gradle hyperlink leads to a 404 Github page

This is the page it should be pointing to, and yes it's referring to

build.gradle.kts

. It's the same as a

build.gradle

file, but written in Kotlin instead of Groovy

Got it thanks

Where have you taken this hyperlink? Is it something in tutorial?

@Alexander Kurasov[JB] Fixed it: https://github.com/JetBrains/compose-jb/pull/1614