No code completion as advertised

I already installed jdk version 17.x.x ++,
and create kotlin source file with ".kt" file extension inside a single Gradle application project folder.

When I write the code, eveything is colorful which is great, but still it misses code completion.
For example if I create a string:

val word ="This is a string"

Then if I write "." for the string it doesn't show the available method that can be used with String class in kotlin.

If I write in intellij idea, if I write word.
At this point intellij will suggest what method is available.

Can you tell me/us how to do like that? like intellij one.