Unity mistaking gameObject for GameObject

Why does it think I typed in GameObject?

Because you cant enable the type GameObject which is what gameObject references. You can use gameObject.SetActive(true/false)

Just to clarify, gameObject refers to the object whereas GameObject refers to the type such as

GameObject.SetActive(true);

will not work,

public GameObject myObject;
myObject.SetActive(true);

will work because the variable defined the type and can reference a specific object.