Why is id 'kotlin-android-extensions' not included by default ? I am new to Kotlin and downloaded Android Studio 2020.3.1 Patch 2 and none of the auto-complete was working because import kotlinx.android.synthetic.main.activity_main.* was not included.

What’s the alternative for current versions ?

Well one might just not want to use them.

Besides they’re deprecated now Android Developers Blog: The future of Kotlin Android Extensions
If you’re just beginning with Kotlin on Android, it’s better you pick another way of referring to views. ViewBinding is considered the default approach now.