It turns out that adding a divider or a space between items in a RecyclerView is non-trivial. You have to extend the RecyclerView.ItemDecoration abstract class and then get into the weeds of the RecyclerView class. It should be simple but this is the state of Android development. I'm sure you'd rather skip over the details and make a simple call as follows:
myRecyclerView.setColoredDivider(dividerColor, dividerHeightPixels) // or myRecyclerView.setVerticalGap(verticalGapInPixels)
If so, then add the com.tazkiyatech:android-utils library to your project and benefit from the Kotlin extension functions defined in the RecyclerViewExtensions.kt file. If you like complexity, then I'll point you to the RecyclerViewColoredDividerItemDecoration.java and RecyclerViewVerticalGapItemDecoration.java files instead.