Is it possible to add a onClick() Event action(in GameObject dropdown) without adding new script in Unity?

Question

I have an MRTK Slate which comes with Pressable Button to close the slate.

When the close button is pressed, the Slate is disabled but not destroyed. This is because in the Events section>Interactable script> GameObject.SetActive() is set by default as shown in fig:

I want to destroy the slate after clicking close button.

I know I can do this by making a script, attaching the slate prefab to the script(or taking the parent of the button till I get slate as parent game object), calling the function, and using GameObject.Destroy().

But I want to understand how the GameObject dropdown in the Interactable script is getting populated :

I understand that the other dropdowns like Transform, Follow me toggle, Solverhandler, etc are displayed because they are attached to the Slate.

But how does the GameObject option is available? This seems a basic thing, but I would like to be sure about how it is coded.

And if it is possible to add my new action in the Gameobject dropdown, if so, how?

I spent time looking at the scripts of Interactable and others, but I am a beginner in C# and was not able to see where is the code which does this.

Any input will help me.