You should use code tags in the future when posting code to make it easier to read.
It looks like GameObject.Find(“denovo”) does not find a GameObject with such a name in the scene and returns null. Then when you try to call GetComponent() on something that does not exist, you get a NullReferenceException.
Finding GameObjects using GameObject.Find is considered bad practice, and it very prone to errors (as you are just finding out). It is a better idea to add the [SerializeField] attribute to the denovo field and then assign the reference using the inspector if it is possible in your case.
If this is not possible, you can create a unique component for your “denovo” button, let’s say DenovoButton, and then you can use FindObjectOfType() to find the reference.