Selectable.interactable

Description

Use to enable or disable the ability to select a selectable UI element (for example, a Button).

Use this or enable the checkbox in the Inspector of a selectable UI element. When disabled, the UI element appears grayed out.

//Attach this script to a GameObject.
//Attach a Button (Create>UI>Button) to the Start Button field in the Inspector of your GameObject.
//In Play mode, press space to toggle the interactability of the Button.

using UnityEngine;
using UnityEngine.UI; // required when using UI elements in scripts

public class Try : MonoBehaviour
{
    //Make sure to attach a Button in the Inspector
    public Button startButton;

    void Update()
    {
        //Press the space key to toggle between the Button being interactable or not
        if (Input.GetKeyDown(KeyCode.Space))
        {
            //Toggle interactable state of the Button on and off
            startButton.interactable = !startButton.interactable;
        }
    }
}