Automatically add an extra product to the cart when a specific product is added in WooCommmerce

functions.php

add_action('woocommerce_before_calculate_totals', 'ensure_two_products_in_cart');
function ensure_two_products_in_cart($cart) {
    if (is_admin() && !defined('DOING_AJAX')) return;

    // Replace '123' with the ID of the product you want to ensure is sold in twos
    $product_id = 123;
    $quantity_to_add = 2;

    foreach ($cart->get_cart() as $cart_item_key => $cart_item) {
        if ($cart_item['product_id'] == $product_id) {
            if ($cart_item['quantity'] < $quantity_to_add) {
                $cart_item['quantity'] = $quantity_to_add;
            }
        }
    }
}