This function queries my website for products associated with the “WordPress Plugin” category and returns them as option HTML using the product ID as the option value and the product name as the label.

/**
 * Get WordPress Product Options for DTX Select Field
 *
 * @return string HTML output of product options for use inside a <select> field or empty string on failure
 */
function au_dtx_demo_get_wordpress_plugin_options()
{
    $products = get_posts(array(
        'fields' => 'ids',
        'post_type' => 'product',
        'post_status' => 'publish',
        'posts_per_page' => -1,
        'orderby' => 'title',
        'order' => 'ASC',
        'ignore_sticky_posts' => false, // move sticky posts to the start of the set
        'tax_query' => array(array(
            'taxonomy' => 'product_cat',
            'field' => 'slug',
            'terms' => 'wordpress-plugin',
            'include_children' => true,
            'operator' => 'IN'
        ))
    ));
    if (is_array($products) && count($products)) {
        $html = '';
        foreach ($products as $product_id) {
            $html .= sprintf('<option value="%s">%s</option>', esc_attr($product_id), esc_html(get_the_title($product_id)));
        }
        return wp_kses($html, wpcf7dtx_get_allowed_field_properties('option'));
    }
    return '';
}
add_shortcode('au_dtx_demo_get_wordpress_plugin_options', 'au_dtx_demo_get_wordpress_plugin_options');

This function was written for demonstration purposes to show that I can return individual values to insert as an option value, label, or the HTML depending on what I set the key attribute to.

/**
 * Get WordPress Product Options for DTX Select Field
 *
 * @param array $atts Shortcode attributes
 *
 * @return string HTML output of option or value for specified key attribute
 */
function au_dtx_demo_shortcode_option($atts)
{
    $atts = shortcode_atts(array('key' => ''), array_change_key_case((array)$atts, CASE_LOWER));
    $atts['key'] = sanitize_text_field($atts['key']);
    if ($atts['key'] == 'value') {
        return esc_attr__('value-from-shortcode', 'aurise');
    } elseif ($atts['key'] == 'label') {
        return esc_html__('Shortcode value!', 'aurise');
    }
    return wp_kses('<option value="hello-world">Hello World!</option>', wpcf7dtx_get_allowed_field_properties('option'));
}
add_shortcode('au_dtx_demo_shortcode_option', 'au_dtx_demo_shortcode_option');