Tutorial On Devsplorer : https://youtu.be/_wI0uPImOlE

Cubifier

using System.Collections;
using UnityEngine;

public class Cubifier : MonoBehaviour
{
    public GameObject TargetCube;

    public Vector3 SectionCount;
    public Material SubCubeMaterial;
    
    private Vector3 SizeOfOriginalCube;
    private Vector3 SectionSize;
    private Vector3 FillStartPosition;
    private Transform ParentTransform;
    private GameObject SubCube;

    void Start()
    {
        if (TargetCube == null)
            TargetCube = gameObject;
        
        SizeOfOriginalCube = TargetCube.transform.lossyScale;
        SectionSize = new Vector3(
            SizeOfOriginalCube.x/SectionCount.x,
            SizeOfOriginalCube.y/SectionCount.y,
            SizeOfOriginalCube.z/SectionCount.z
            ) ;

        FillStartPosition = TargetCube.transform.TransformPoint(new Vector3(-0.5f, 0.5f, -0.5f))
                            + TargetCube.transform.TransformDirection( new Vector3(SectionSize.x,-SectionSize.y,SectionSize.z)/2.0f);
        
        ParentTransform = new GameObject(TargetCube.name + "CubeParent").transform;
        
        StartCoroutine(DivideIntoCuboids());
        //InstantDivideIntoCuboids();
    }

    #region AnimatedAppear

    void Looper()
    {
        Destroy(ParentTransform.gameObject);
        ParentTransform = new GameObject(TargetCube.name + "Parent").transform;

        StartCoroutine(DivideIntoCuboids());

    }
    
    IEnumerator DivideIntoCuboids()
    {
        for (int i = 0; i < SectionCount.x; i++)
        {
            for (int j = 0; j < SectionCount.y; j++)
            {
                for (int k = 0; k < SectionCount.z; k++)
                { 
                    SubCube =  GameObject.CreatePrimitive(PrimitiveType.Cube) ;

                    SubCube.transform.localScale = SectionSize;
                    SubCube.transform.position = FillStartPosition + 
                                                   TargetCube.transform.TransformDirection( new Vector3((SectionSize.x) * i , -(SectionSize.y) * j,(SectionSize.z) * k));
                    SubCube.transform.rotation = TargetCube.transform.rotation;

                    SubCube.transform.SetParent(ParentTransform);
                    SubCube.GetComponent<MeshRenderer>().material = SubCubeMaterial;

                    yield return new WaitForSeconds(0.1f);
                }
            }
        }
        Destroy(TargetCube);

        
        // foreach (Transform subCube in ParentTransform)
        // {
        // subCube.gameObject.AddComponent<Rigidbody>();
        // }
        
        //Looper();
    }

    #endregion
    
    void InstantDivideIntoCuboids()
    {
        for (int i = 0; i < SectionCount.x; i++)
        {
            for (int j = 0; j < SectionCount.y; j++)
            {
                for (int k = 0; k < SectionCount.z; k++)
                { 
                    SubCube =  GameObject.CreatePrimitive(PrimitiveType.Cube) ;
                    SubCube.transform.localScale = SectionSize;
                    SubCube.transform.position = FillStartPosition + 
                                                   TargetCube.transform.TransformDirection( new Vector3((SectionSize.x) * i , -(SectionSize.y) * j,(SectionSize.z) * k));
                    SubCube.transform.rotation = TargetCube.transform.rotation;

                    SubCube.transform.SetParent(ParentTransform);
                    SubCube.GetComponent<MeshRenderer>().material = SubCubeMaterial;

                }
            }
        }
        Destroy(TargetCube);

        
        // foreach (Transform subCuboid in ParentTransform)
        // {
        // subCuboid.gameObject.AddComponent<Rigidbody>();
        // }
        
        //Looper();
    }
}