add_filter( 'aioseo_llms_term_description', 'aioseo_filter_llms_term_description', 10, 2 );

function aioseo_filter_llms_term_description( $description, $term = null ) {

    if ( is_a( $term, 'WP_Term' ) && 'category' === $term->taxonomy && $term->count > 0 ) {

        $description .= ' This category contains ' . $term->count . ' posts.';

    }

    return $description;

}