WordPress: Add the aria-label attribute to wp_dropdown_categories(): https://www.n7studios.co.uk/adding-aria-labels-wp_dropdown_categories/

wp-dropdown-categories-aria-label.php

<?php
/**
 * If the aria-label argument has been specified in a wp_dropdown_categories() call,
 * output the aria-label option in the <select>
 *
 * @since   1.0.0
 *
 * @param   string  $output     HTML Output
 * @param   array   $arguments  wp_dropdown_category() arguments
 * @return  string              Modified HTML Output
 */
function wp_dropdown_cats_aria_label_support( $output, $arguments ) {

    // Bail if no aria-label argument has been supplied
    if ( ! isset( $arguments['aria-label'] ) ) {
        return $output;
    }

    // Add aria-label
    $output = str_replace( '<select ', '<select aria-label="' . sanitize_text_field( $arguments['aria-label'] ) . '"', $output );

    // Return
    return $output;

}
add_filter( 'wp_dropdown_cats', 'wp_dropdown_cats_aria_label_support', 10, 2 );