Example to how to place a game object in AR mobile

ARObjectHitDetect.cs

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.XR.ARFoundation;
using UnityEngine.XR.ARSubsystems;

[RequireComponent(typeof(ARRaycastManager))]
public class ARObjectHitDetect : MonoBehaviour
{

    private RaycastHit _Rhit;
    private bool _Hit;
    
    void Awake()
    {
    }

    void Update()
    {
        if (Input.touchCount > 0)
        {
            Touch touch = Input.GetTouch(0);
            if (touch.phase == TouchPhase.Began || touch.phase == TouchPhase.Moved)
            {
                Ray ray = Camera.main.ScreenPointToRay(touch.position);
                _Hit = false;
                // See if we "touched" anything in the AR world within 16m
                if (Physics.Raycast(ray, out _Rhit, 16.0f))
                {
                    _Hit = true;
                    Debug.Log($"We hit {_Rhit.transform.name}");
                    if (_Rhit.rigidbody != null)
                    {
                        Debug.Log($"We hit a rigibody {_Rhit.rigidbody.name}");
                    }
                }
            }
        }
    }
    
    void FixedUpdate()
    {
        if (_Hit)
        {
            Debug.Log("Proocess physics etc on the "touched" AR object");
            Transform hitTransform = _Rhit.transform;
            Rigidbody hitRigidbody = _Rhit.rigidbody.GetComponent<Rigidbody>();
            Vector3 hitPosition = _Rhit.point;
            // ...
        }
    }
}

ARObjectPlacement.cs

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.XR.ARFoundation;
using UnityEngine.XR.ARSubsystems;

[RequireComponent(typeof(ARRaycastManager))]
public class ARObjectPlacement : MonoBehaviour
{

    private ARRaycastManager raycastManager;

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

    void Update()
    {
        if (Input.touchCount > 0)
        {
            Touch touch = Input.GetTouch(0);
            if (touch.phase == TouchPhase.Began || touch.phase == TouchPhase.Moved)
            {
                if (raycastManager != null)
                {
                    if (raycastManager.Raycast(touch.position, hits, TrackableType.PlaneWithinPolygon))
                    {
                        Pose hitPose = hits[0].pose;
                        // Instantiate Game Object at hitPose.position
                        // Optional set rotation of instantiated Game Object
                    }|
                }
            }
        }
    }
}