There is an error when following steps to use the nav_version variable in project’s build.gradle of Penny_Drop.

Following the official documentation the way to use this variable is adding in the app’s build.gradle file: https://developer.android.com/guide/navigation/navigation-getting-started

dependencies {
  def nav_version = "2.3.5"

  implementation "androidx.navigation:navigation-fragment:$nav_version"
  implementation "androidx.navigation:navigation-ui:$nav_version"

  .......
}