How to weld mesh vertices in the runtime

I took a look at this post https://answers.unity.com/questions/1382854/welding-vertices-at-runtime.html to weld vertices.

Answer of user @imaxus is right but there is a problem with lights and normals. Answer of @Bunny83 does not work. Why? Can someone explain why?

I used the user imaxus's code. But there is a issue with lighting and normals. How to fix?

 public static Mesh WeldVertices(Mesh aMesh, float aMaxDelta = 0.01f) {
                var verts = aMesh.vertices;
                var normals = aMesh.normals;
                var uvs = aMesh.uv;
                Dictionary<Vector3, int> duplicateHashTable = new Dictionary<Vector3, int>();
                List<int> newVerts = new List<int>();
                int[] map = new int[verts.Length];
    
                //create mapping and find duplicates, dictionaries are like hashtables, mean fast
                for (int i = 0; i < verts.Length; i++) {
                    if (!duplicateHashTable.ContainsKey(verts[i])) {
                        duplicateHashTable.Add(verts[i], newVerts.Count);
                        map[i] = newVerts.Count;
                        newVerts.Add(i);
                    }
                    else {
                        map[i] = duplicateHashTable[verts[i]];
                    }
                }
    
                // create new vertices
                var verts2 = new Vector3[newVerts.Count];
                var normals2 = new Vector3[newVerts.Count];
                var uvs2 = new Vector2[newVerts.Count];
                for (int i = 0; i < newVerts.Count; i++) {
                    int a = newVerts[i];
                    verts2[i] = verts[a];
                    normals2[i] = normals[a];
                    uvs2[i] = uvs[a];
                }
                // map the triangle to the new vertices
                var tris = aMesh.triangles;
                for (int i = 0; i < tris.Length; i++) {
                    tris[i] = map[tris[i]];
                }
                aMesh.triangles = tris;
                aMesh.vertices = verts2;
                aMesh.normals = normals2;
                aMesh.uv = uvs2;
    
                aMesh.RecalculateBounds();
                aMesh.RecalculateNormals();
    
                return aMesh;
            }

Then I took a look at Bunny83's code, but it did not work nd even it did not give and error. How to fix this? HELP PLEASE

 public static void WeldVertices(Mesh aMesh, float aMaxDelta = 0.001f)
    {
        var verts = aMesh.vertices;
        var normals = aMesh.normals;
        var uvs = aMesh.uv;
        List<int> newVerts = new List<int>();
        int[] map = new int[verts.Length];
        // create mapping and filter duplicates.
        for(int i = 0; i < verts.Length; i++)
        {
            var p = verts[i];
            var n = normals[i];
            var uv = uvs[i];
            bool duplicate = false;
            for(int i2 = 0; i2 < newVerts.Count; i2++)
            {
                int a = newVerts[i2];
                if (
                    (verts[a] - p).sqrMagnitude <= aMaxDelta && // compare position
                    Vector3.Angle(normals[a], n) <= aMaxDelta && // compare normal
                    (uvs[a] - uv).sqrMagnitude <= aMaxDelta // compare first uv coordinate
                    )
                {
                    map[i] = i2;
                    duplicate = true;
                    break;
                }
            }
            if (!duplicate)
            {
                map[i] = newVerts.Count;
                newVerts.Add(i);
            }
        }
        // create new vertices
        var verts2 = new Vector3[newVerts.Count];
        var normals2 = new Vector3[newVerts.Count];
        var uvs2 = new Vector2[newVerts.Count];
        for(int i = 0; i < newVerts.Count; i++)
        {
            int a = newVerts[i];
            verts2[i] = verts[a];
            normals2[i] = normals[a];
            uvs2[i] = uvs[a];
        }
        // map the triangle to the new vertices
        var tris = aMesh.triangles;
        for(int i = 0; i < tris.Length; i++)
        {
            tris[i] = map[tris[i]];
        }
        aMesh.vertices = verts2;
        aMesh.normals = normals2;
        aMesh.uv = uvs2;
        aMesh.triangles = tris;
    }

@Bunny83 can you help me why with your code does not work?