Access UI in scene from an instance prefab

Hi, I’m trying to access a UI element in my scene from an instance but not having much luck. I’ve managed to not get any errors with this script below but it doesn’t SetActive a ui elements or pass variables back.
My code on the prefab:-

public class NetworkRoomPlayerLobby : NetworkBehaviour
{
private Button startGameButton = null;
private GameObject gameButton = null;
private GameObject lobbyUI = null;
private TMP_Text playerNameTexts = null;
private TMP_Text playerReadyTexts = null;

    [SyncVar(hook = nameof(HandleDisplayNameChanged))]
    public string DisplayName = "Loading...";
    [SyncVar(hook = nameof(HandleReadyStatusChanged))]
    public bool IsReady = false;

    private bool isLeader;

    private void Awake()
    {            
        lobbyUI = GameObject.FindGameObjectWithTag("Panel_Lobby");
        playerNameTexts = lobbyUI.GetComponentInChildren<TMP_Text[]>();
        playerReadyTexts = lobbyUI.GetComponentInChildren<TMP_Text[]>();
        playerNameTexts = new TMP_Text[4];
        playerReadyTexts = new TMP_Text[4];
        gameButton = GameObject.FindGameObjectWithTag("StartButton");
        Button startGameButton = gameButton.GetComponentInChildren<Button>();
    }

Here is the code for the UI menu script:-

public class MainMenu : MonoBehaviour
{
[SerializeField] private NetworkManager networkManager;

    [Header("UI")]
    public GameObject lobbyUI = null;
    public TMP_Text[] playerNameTexts = null;
    public TMP_Text[] playerReadyTexts = null;
    public Button gameButton = null;
    [SerializeField] private GameObject landingPagePanel = null;
    

    public void HostLobby()
    {            
        networkManager.StartHost();            
        landingPagePanel.SetActive(false);            
    }        
}

I personally use singletons to find scripts.

using UnityEngine;

public class FindMe : MonoBehaviour
{
      public static FindMe singleton;
      void Awake()
      {
              singleton = this;
      }
}

The object will be found anywhere in the scene if it exists without any performance problems.

using UnityEngine;
        
public class TriesToAccessFindMe : MonoBehaviour
{
       FindMe f;
       void Start()
       {
               f = FindMe.singleton;
        }
}

The second script shows how you find the script.

Greetings,
Max