WordPress does not have a builtin function named get_all_category_ids(). However, you can easily retrieve all category IDs by using a custom function that queries the WordPress database. Here's an example of how you can create such a function:

function get_all_category_ids() {
    $args = array(
        'taxonomy' => 'category',
        'hide_empty' => false,
    );

    $categories = get_categories($args);
    $category_ids = array();

    foreach ($categories as $category) {
        $category_ids[] = $category>term_id;
    }

    return $category_ids;
}

Here's how this function works:

1. It defines an array of arguments for the get_categories() function. The taxonomy argument is set to 'category', and hide_empty is set to false to include categories that have no posts.

2. It calls get_categories() to retrieve all categories based on the provided arguments.

3. It loops through the returned categories, extracts the term_id (which is the category ID), and adds it to an array.

4. Finally, it returns the array of category IDs.

You can use this get_all_category_ids() function in your WordPress theme or plugin to get an array of all category IDs on your site.