A script that listens to trackable changed events for the ARAnchor manager and can recall saved anchors when an application is relaunched.

AnchorRecallManager.cs

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

public class AnchorRecallManager : MonoBehaviour
{
    [SerializeField]
    ARAnchorManager m_AnchorManager;
    const float k_WaitDelay = 1.0f;

    [SerializeField]
    GameObject m_AnchorVisualObjectPrefab;

    List<ARSaveOrLoadAnchorResult> m_LoadResults = new();

    public static Dictionary<TrackableId, SerializableGuid> savedGuidsByTrackableId = new();

    void OnEnable()
    {
        m_AnchorManager.trackablesChanged.AddListener(OnAnchorsChanged);
    }

    void OnDisable()
    {
       m_AnchorManager.trackablesChanged.RemoveListener(OnAnchorsChanged); 
    }

    IEnumerator Start()
    {
        yield return new WaitForSeconds(k_WaitDelay);

        foreach(var anchor in m_AnchorManager.trackables)
        {
            var visualObject = Instantiate(m_AnchorVisualObjectPrefab, anchor.transform.position, anchor.transform.rotation);
            visualObject.transform.SetParent(anchor.transform);
        }

        if (m_AnchorManager.descriptor.supportsLoadAnchor)
            LoadAllAnchors();
    }

    async void LoadAllAnchors()
    {
        try
        {
            var anchorDict = await AnchorSaveFile.instance.GetSavedAnchorsDataAsync();
            await m_AnchorManager.TryLoadAnchorsAsync(anchorDict.Keys, m_LoadResults, null);

            foreach (var result in m_LoadResults)
            {
                if (result.resultStatus.IsError())
                {
                    Debug.LogError($"Failed to load an anchor with status {result.resultStatus}");
                    continue;
                }

                savedGuidsByTrackableId[result.anchor.trackableId] = result.savedAnchorGuid;
            }
        }
        catch (OperationCanceledException)
        {
            Debug.LogError("Load operation was cancelled.");
        }
        finally
        {
            m_LoadResults.Clear();
        }
    }

    void OnAnchorsChanged(ARTrackablesChangedEventArgs<ARAnchor> eventArgs)
    {
        foreach (var anchor in eventArgs.added)
        {
            Debug.Log($"Anchor added: {anchor.trackableId}");
            var visualObject = Instantiate(m_AnchorVisualObjectPrefab, anchor.transform.position, anchor.transform.rotation); 
            visualObject.transform.SetParent(anchor.transform);
        }
        foreach (var anchor in eventArgs.updated)
        {
            Debug.Log($"Anchor updated: {anchor.trackableId}");
        }
    }
}