Android: fix for DialogFragment's size issues when a recyclerView lives inside it. This extension method allows you to hardcode in the desired dimensions of the dialog fragment as percentages of the available screen real estate.

dialogFragmentSizeFix.kt

/**
 * For dialogFragments with size issues, say due to a recyclerView inside them,
 * use this extension function in their onResume() callback method.
 * Provide the desired percentages of with and height of the available screen space
 * which you desire the dialog to occupy, and enjoy your day.
 */
fun DialogFragment.fixDialogSize(widthPercent: Double, heightPercent: Double){
    val size = Point()
    dialog?.window?.apply {
        windowManager.defaultDisplay.getSize(size)

        setLayout(widthPercent of size.x, heightPercent of size.y)
        setGravity(Gravity.CENTER)
    }
}

private infix fun Double.of(value: Int) = (this * value).toInt()

UsageSampleDialogFragment.kt

class HelpDialogFragment : androidx.fragment.app.DialogFragment() {

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_help, null)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        recycler.adapter = HelpAdapter().apply {
            setItems(getRules())
        }
        recycler.layoutManager = LinearLayoutManager(requireActivity())

    }

    override fun onResume() {
        super.onResume()

        fixDialogSize(0.98, 0.9)
    }

}

Still useful.
Thumbs up for solution.
Thanks.