CombineMeshes.cs

private MeshFilter filter;

    public void CombineGridPointMeshes()
    {
        combineInstances.Clear();

        HashSet<MeshFilter> meshes = new HashSet<MeshFilter>(gridPointMeshes);

        foreach (MeshFilter filter in meshes)
        {
            if (filter.sharedMesh == null) continue;

            CombineInstance combineInstance = new()
            {
                mesh = filter.sharedMesh,
                transform = transform.worldToLocalMatrix * filter.transform.localToWorldMatrix
            };

            combineInstances.Add(combineInstance);
        }

        //[ COMBINE MESHES ]
        Mesh combinedMesh = new();

        combinedMesh.indexFormat = UnityEngine.Rendering.IndexFormat.UInt32;

        combinedMesh.CombineMeshes(combineInstances.ToArray());

        filter = chunkMesh.GetComponent<MeshFilter>();
        filter.sharedMesh = combinedMesh;
        filter.gameObject.isStatic = true;

        combinedMesh.name = type + "_" + worldPos.x + "_" + worldPos.y + "_" + worldPos.z + "_" + "MESH";

        //chunkMeshCollider.sharedMesh = combinedMesh;
    }