Part 1 of the script to place holograms based on raycasts with AR Foundation

ARPlaceHologram.cs

public class ARPlaceHologram : MonoBehaviour
{
    // The prefab to instantiate on touch.
    [SerializeField]
    private GameObject _prefabToPlace;

    // Cache ARRaycastManager GameObject from ARCoreSession
    private ARRaycastManager _raycastManager;

    // List for raycast hits is re-used by raycast manager
    private static readonly List<ARRaycastHit> Hits = new List<ARRaycastHit>();

    void Awake()
    {
        _raycastManager = GetComponent<ARRaycastManager>();
    }