An example of a custom graph that extends A* Pathfinding Project to directly use a Unity Tilemap for building nodes and navigation. Also uses https://gist.github.com/thebeardphantom/6a05ef68ce6ce7c890c4a4d9afaccf74

TilemapGraph.cs

using Pathfinding;
using Pathfinding.Serialization;
using Pathfinding.Util;
using System;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.Tilemaps;

[Preserve]
[JsonOptIn]
public class TilemapGraph : NavGraph
{
    #region Types

    public class TilemapGraphNode : PointNode
    {
        #region Fields

        public Vector2Int TilemapCell;

        #endregion

        #region Constructors

        public TilemapGraphNode(AstarPath astar) : base(astar) { }

        public TilemapGraphNode() { }

        #endregion
    }

    #endregion

    #region Fields

    public Tilemap WorldTilemap;

    private TilemapGraphNode[] _nodes;

    #endregion

    #region Methods

    private static bool CheckNodePositionWalkable(TilemapGraphNode node)
    {
        return true;
    }

    /// <inheritdoc />
    public override void GetNodes(Action<GraphNode> action)
    {
        if (_nodes == null)
        {
            return;
        }

        foreach (var node in _nodes)
        {
            action(node);
        }
    }

    /// <inheritdoc />
    protected override IEnumerable<Progress> ScanInternal()
    {
        if (WorldTilemap == null)
        {
            yield break;
        }

        WorldTilemap.CompressBounds();
        var bounds = WorldTilemap.cellBounds;

        var nodeGrid = new Dictionary<Vector2Int, TilemapGraphNode>();

        foreach (var tilemapPosition in bounds.allPositionsWithin)
        {
            if (!WorldTilemap.HasTile(tilemapPosition))
            {
                continue;
            }

            var node = new TilemapGraphNode(active)
            {
                TilemapCell = tilemapPosition.To2D()
            };
            node.position = GetAStarPosition(node.TilemapCell);
            node.Walkable = CheckNodePositionWalkable(node);

            nodeGrid.Add(node.TilemapCell, node);
            yield return new Progress(0f, "Generating nodes");
        }

        var connectionList = new List<Connection>(6);
        var index = 0;
        var nodeCount = nodeGrid.Count;
        foreach (var node in nodeGrid.Values)
        {
            connectionList.Clear();

            foreach (var direction in EnumData<HexNeighborDirection>.Values)
            {
                var neighborCell = node.TilemapCell.GetNeighborCell(direction);
                if (nodeGrid.TryGetValue(neighborCell, out var newConnection))
                {
                    connectionList.Add(new Connection(newConnection, initialPenalty));
                }
            }

            node.connections = connectionList.ToArray();
            node.SetConnectivityDirty();
            yield return new Progress((float) index++ / nodeCount, "Forming connections");
        }

        _nodes = nodeGrid.Values.ToArray();
    }

    private Int3 GetAStarPosition(Vector2Int tilemapPosition)
    {
        return (Int3) (Vector3) WorldTilemap.layoutGrid.GetCellCenterWorld2D(tilemapPosition);
    }

    #endregion
}