MouseOverDetector.cs

using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

[RequireComponent(typeof(Graphics))]
public class MouseOverDetector : MonoBehaviour{

    [SerializeField] private GraphicRaycaster raycaster;    //  Required
    [SerializeField] private EventSystem eventSystem;       //  Required

    /// <summary>
    /// マウスカーソルがこのUI上に存在するか
    /// </summary>
    /// <returns></returns>
    public bool IsMouseOver()
    {
        List<RaycastResult> results = new List<RaycastResult>();
        PointerEventData eventData = new PointerEventData(eventSystem);
        eventData.position = Input.mousePosition;

        raycaster.Raycast(eventData, results);

        return results.Any(result => result.gameObject == gameObject);
    }
}