A script that places and manages Anchors, checking if the platform supports saved anchors and writing the ID to a file.

AnchorPlacementManager.cs

using UnityEngine;
using UnityEngine.InputSystem;
using UnityEngine.XR.ARFoundation;
using UnityEngine.XR.ARFoundation.Samples;

public class AnchorPlacementManager : MonoBehaviour
{
    [SerializeField]
    ARAnchorManager m_AnchorManager;

    [SerializeField]
    GameObject m_AnchorPrefab;

    void Update()
    {
#if UNITY_EDITOR
        // place anchor with middle of camera raycast
        if (Mouse.current.leftButton.wasPressedThisFrame)
        {
            if (Physics.Raycast(Camera.main.transform.position, Camera.main.transform.forward, out RaycastHit hit))
            {
                PlaceAnchor(hit.point, Quaternion.LookRotation(hit.normal));
            }
        }
#endif
    }
    
    async Awaitable SaveAnchorAsync(ARAnchor anchor)
    {
        var result = await m_AnchorManager.TrySaveAnchorAsync(anchor);
        if (result.status.IsError())
        {
            Debug.LogError($"Failed to save anchor {anchor.trackableId} with status {result.status}");
            return;
        }

        Debug.Log($"Successfully saved anchor {anchor.trackableId}");
        AnchorRecallManager.savedGuidsByTrackableId[anchor.trackableId] = result.value;
        await AnchorSaveFile.instance.SaveAnchorIdAsync(result.value);
    }

    public async void RemoveAnchor(ARAnchor anchor)
    {
        // Erase the persistent storage associated with the anchor
        try
        {
            if (m_AnchorManager.descriptor.supportsEraseAnchor)
                await EraseAnchorAsync(anchor);
        }
        catch (OperationCanceledException)
        {
            // Do nothing
        }

        // Stop tracking the anchor
        var result = m_AnchorManager.TryRemoveAnchor(anchor);
        if (result)
        {
           Debug.Log(anchor.trackableId + " Anchor removed"); 
        }
    }

    async Awaitable EraseAnchorAsync(ARAnchor anchor)
    {
        if (!AnchorRecallManager.savedGuidsByTrackableId.TryGetValue(anchor.trackableId, out var savedGuid))
        {
            Debug.LogError($"Failed to erase saved data for anchor: {anchor.trackableId}");
        }
        else
        {
            var result = await m_AnchorManager.TryEraseAnchorAsync(savedGuid);
            if (result.IsSuccess())
            {
                Debug.Log($"Successfully erased anchor {anchor.trackableId}");
                await AnchorSaveFile.instance.EraseAnchorIdAsync(savedGuid);
                AnchorRecallManager.savedGuidsByTrackableId.Remove(anchor.trackableId);
            }
            else
                Debug.LogError($"Erase operation failed for anchor {anchor.trackableId}");
        }
    }

    public void RemoveAllAnchors()
    {
        TrackableCollection<ARAnchor> currentSetOfAnchors = m_AnchorManager.trackables;
        foreach(var anchor in currentSetOfAnchors)
        {
            RemoveAnchor(anchor);
        }
    }
}