How To Load wp_add_inline_styles

You need to add enqueue your child themes style sheet as well

add_action( 'wp_enqueue_scripts', 'inline_bar_width' );
function inline_bar_width() {

wp_enqueue_style( 'twentytwenty-style', get_stylesheet_directory_uri() . '/style.css' );

if ( is_category( 'ratings' ) ) {

    $bar = bar_width();

    $css="";

    $css .= sprintf('.bar {width: %s%%;}', $bar );

    if ( $css ) {
        wp_add_inline_style( 'twentytwenty-style', $css );
    }
  }
}