DropDownSelect.cs

using TMPro;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
using static TMPro.TMP_Dropdown;

public class DropDownSelect : MonoBehaviour
{
    void Update ()
    {
        TMP_Dropdown dropMusics = GetComponent<TMP_Dropdown>();
        if (dropMusics.IsExpanded && EventSystem.current.currentSelectedGameObject != null)
        {
            string selected = EventSystem.current.currentSelectedGameObject.GetComponentInChildren<TextMeshProUGUI>()?.text;
            Scrollbar scroll = GameObject.Find("Dropdown List").GetComponentInChildren<Scrollbar>();

            int count = 0;
            foreach (OptionData pos in dropMusics.options)
            {
                if (pos.text == selected)
                {
                    scroll.value = 1f - ((float)count / (dropMusics.options.Count-1));
                    break;
                }
                count++;
            }
        }
    }
}