Where is the category group ID

I am not sure if this is a bug or not (or the problem is between the chair and the keyboard) but I am unable to find the “category_group” ID when I create a new Category Group in admin.php -> Developer -> Categories.

On this page I’ve created a New Category Group called “test123” and in this New Category Group I have created Category-1, Category-2, Category-3.

I’ve also nested them and added entries to them (my test category group is assigned to a “test-channel”) but I cannot list them using:

{exp:channel:categories channel="test-channel" category_group="where-is-this-id?"}
    {category_name}
{/exp:channel:categories}

I’ve read the documentation multiple times but still I am unable to find the ID.

Thank you.