2D GameObject Array to 2D List

I have a 2D GameObject array, and I want to convert it into a 2D GameObject List. Using .ToList() gives a error. Is there a way to use something like .ToList() to convert this array, or will I have to craft the list from the array myself?

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 
 public class Test : MonoBehaviour {
 
     private GameObject[][] array2D;
     private List<List<GameObject>> list2D = new List<List<GameObject>>();
 
     void Update () {
         array2D = list2D.ToList ();
     }
 }

The error the console gives is:

 Cannot implicitly convert type `System.Collections.Generic.List<UnityEngine.GameObject[]>' to `System.Collections.Generic.List<System.Collections.Generic.List<UnityEngine.GameObject>>'