With the code below, I calculate and displays the total subsidies amount based on cart item shipping class and quantity:

/**
 * Utility function: Get shipping class subsidy amount
 * 
 * @return float
 */
function get_shipping_class_subsidy_amount( $shipping_class ) {
    // return a float number for '12-50' case
    if ( false !== strpos($shipping_class, '12-50') ) {
        return 12.5;
    }
    // Extract the integer from the slug
    else {
        return preg_replace('/D/', '',  $shipping_class);
    }
}

/**
 * Utility function: Get total subsidies amount
 * 
 * @return float
 */
function get_total_subsidies( $cart_items ){
    $total_subsidy = 0; // Initializing

    // Loop through cart items
    foreach ( $cart_items as $item ){
        $subsidy = (float) get_shipping_class_subsidy_amount( $item['data']->get_shipping_class() );
        $price = get_post_meta($values['product_id'] , '_price', true);
        if ( $subsidy > 0 ) {
            $total_subsidy += $item['quantity'] * $subsidy;
        }
    }
    return $total_subsidy;
}


/**
 * Display HTML formatted total subsidies amount in classic cart and checkout pages.
 * Hooked function.
 */
function display_total_subsidies() {
    if ( $total_subsidy = get_total_subsidies( WC()->cart->get_cart() ) ) {
        echo '<tr class="subsidies">
            <th>' . esc_html__( 'Subsidies', 'woocommerce' ) . '</th>
            <td data-title="' . esc_html__( 'Subsidies', 'woocommerce' ) . '">' . wc_price($total_subsidy) . '</td>
        </tr>';
    }
}

add_action ( 'woocommerce_cart_totals_before_shipping', 'display_total_subsidies', 10 ); // for Cart page
add_action ( 'woocommerce_review_order_before_shipping', 'display_total_subsidies', 10 ); // for Checkout page

The problem is that the cart item subsidy amount is obtained twice when it’s a bundle product, as it takes into account the bundled product itself and it’s products components.

But the calculation in the label is correct.