Public variable not appearing in the inspector (C#)

Why isn't this public variable being showed in the inspector?

 public class controleInventario : MonoBehaviour {
     
     [System.Serializable]
     public class Configuracoes {
         
         public int Espacamento;
         public Vector2 posicaoNaTela;
         public int Altura, Largura;
         public int larguraIcone, alturaIcone;
         public int Linhas, Colunas;
         
         [HideInInspector]
         public Rect retanguloFinal;
         
     }
     
     [System.Serializable]
     public class icones {
         
         public Texture2D Nulo = null;
         public Texture2D Machado;
         public Texture2D Espada;
         public Texture2D Amuleto;
         
     }
     
     [System.Serializable]
     public class objetos {
         
         public GameObject Nulo = null;
         public GameObject Machado;
         public GameObject Espada;
         public GameObject Amuleto;
         
     }
     
     public Configuracoes configInventario;
     public icones Icones;
     public objetos Objetos;
     public slot[] Slots; // THIS ONE!
     
     public bool inventarioAberto;
     public KeyCode teclaDeAbertura;

[...]

And here's the slot class:

 public class slot {
 
         public int itemID;
         public Texture2D representacaoGrafica;
         public GameObject objetoReferente;
         public int quantidadeNesteSlot;
         public Rect Posicao;
         public bool emUso;
 
 }

Here's the image that show the variable not being displayed:

Can someone explain me this? Thanks from now!