Gradle is installed:
I went through the standard New Project|Kotlin:

A JDK was selected and besides that I used the defaults:

Now we see the new project: but where's the build.gradle.kts ?

To create a gradle based project (in kotlin) you have to select
New Project->Gradle->Check Kotlin DSL BuildScript->Kotlin/JVM
If you uncheck the Kotlin DSL BuildScript then build.gradle is created while when checking it you'll find a build.gradle.kts file
Like this:

PS:
If you want to migrate existing project with Groovy gradle to Kotlin DSL check this out https://medium.com/mindorks/migrating-gradle-build-scripts-to-kotlin-dsl-89788a4e383a
If you want to add gradle to existing non-gradle project right click on project in project structure and then add support for gradle from there
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