How to remove bottom line in android SearchView component?

When you get a reference to your SearchView; This will work:

val backgroundView = searchView.findViewById(android.support.v7.appcompat.R.id.search_plate) as View
backgroundView.background = null

<androidx.appcompat.widget.SearchView
  app:queryBackground="@null"
  ...
/>

Setting this to @null in your XML will remove the colored bar.