Woocommerce: Best way to iterate through orders and order products

Question

I'm getting all the processing orders and then I need to iterate through each order to perform certain actions, the only way I have found to do this is to use a nested loop:

foreach ( $processing_orders as $order ) {
            
            foreach( $order->get_items() as $item ) {
                //Do stuff
            }
}

Our woocommerce store has grown incredibly, and now this $processing_orders array has thousand of processing orders, we have a performance bottleneck here, and I'm worried about the scalability of this in the future, I wonder if there's a better way to do this without the need to use a nested loop.

UPDATE As requested Im adding the full code:

global $woocommerce;

    // Create a mailer
    $mailer = $woocommerce->mailer();

    $processing_orders = (array) wc_get_orders( array(
        'limit'        => -1,
        'status'       => ['wc-processing','wc-follow-up','wc-follow-up-2','wc-follow-up-3','wc-follow-up-4'],
        'type' => 'shop_order',
        'date_created' => '>'. $from
    ) );

    if ( sizeof($processing_orders) > 0 ) {
        $reminder_text = __("Notificación: fecha de envío enviada al proveedor $today", "woocommerce");

        foreach ( $processing_orders as $order ) {
            
            foreach( $order->get_items() as $item ) {
                $product_id = $item->get_product_id();
                $current_shipping_days = get_post_meta( $product_id, '_shipping_days_field', true );
                $current_shipping_days = (int)$current_shipping_days;
                $product_shipping_date = convertDateTimeImmutable($order->get_date_created())->modify( "+ $current_shipping_days weekdays" )->format( 'd/m/y' );

                $days_until_shipping = $date2->diff($date1)->format("%a");  //find difference
                $days = intval($diff);

                $product_post_object = get_post( $product_id );
                $vendor_id = $product_post_object->post_author;

                $vendor_info = get_userdata( $vendor_id );
                $vendor_email = $vendor_info->user_email;

                $order_url = esc_url( add_query_arg( array(
                    'order_id'   => $order->get_order_number(),
                    '_view_mode' => 'email',
                    'permission' => '1',
                ), dokan_get_navigation_url( 'orders' ) ) );

                switch ($days) {
                    case 3:
                        $message_body = '<p>'.sprintf( __("Faltan 3 días para que se cumpla la fecha de entrega de tu pedido: %s"), 
                                            '<a href="'.esc_url( $order_url ).'">#'.$order->get_order_number().'</a>'
                                        ) .'</p>';

                        $message = $mailer->wrap_message(
                        // Message head and message body.
                        sprintf( '<h2>'. __( 'Faltan 3 días para que se cumpla la fecha de entrega del pedido %s' ) . '</h2>', $order->get_order_number() ), $message_body );

                        // Cliente email, email subject and message.
                        $mailer->send( $vendor_email, sprintf( __( 'Aviso: pedido #%s, faltan 3 días para que se cumpla la fecha de entrega' ), $order->get_order_number() ), $message );
                        break;
                    case 2:
                        $message_body = '<p>'.sprintf( __("Faltan 2 días para que se cumpla la fecha de entrega de tu pedido: %s"), 
                                            '<a href="'.esc_url( $order_url ).'">#'.$order->get_order_number().'</a>'
                                        ) .'</p>';

                        $message = $mailer->wrap_message(
                        // Message head and message body.
                        sprintf( '<h2>'. __( 'Faltan 2 días para que se cumpla la fecha de entrega del pedido %s' ) . '</h2>', $order->get_order_number() ), $message_body );

                        // Cliente email, email subject and message.
                        $mailer->send( $vendor_email, sprintf( __( 'Aviso: pedido #%s, faltan 2 días para que se cumpla la fecha de entrega' ), $order->get_order_number() ), $message );
                        break;
                    case 1:
                        $message_body = '<p>'.sprintf( __("Falta 1 día para que se cumpla la fecha de entrega del pedido: %s"), 
                                            '<a href="'.esc_url( $order_url ).'">#'.$order->get_order_number().'</a>'
                                        ) .'</p>';

                        $message = $mailer->wrap_message(
                        // Message head and message body.
                        sprintf( '<h2>'. __( 'Falta 1 día para que se cumpla la fecha de entrega del pedido %s' ) . '</h2>', $order->get_order_number() ), $message_body );

                        // Cliente email, email subject and message.
                        $mailer->send( $vendor_email, sprintf( __( 'Aviso: pedido #%s, falta 1 día para que se cumpla la fecha de entrega' ), $order->get_order_number() ), $message );
                        break;
                    case 0:
                        $message_body = '<p>'.sprintf( __("Hoy se cumple la fecha de entrega del pedido: %s"), 
                                            '<a href="'.esc_url( $order_url ).'">#'.$order->get_order_number().'</a>'
                                        ) .'</p>';

                        $message = $mailer->wrap_message(
                        // Message head and message body.
                        sprintf( '<h2>'. __( 'Aún no has enviado el pedido %s Hoy se cumple la fecha de entrega. Enviar los pedidos tarde tiene consecuencias.' ) . '</h2>', $order->get_order_number() ), $message_body );

                        // Cliente email, email subject and message.
                        $mailer->send( $vendor_email, sprintf( __( 'Aviso: pedido #%s, hoy se cumple la fecha para la entrega' ), $order->get_order_number() ), $message );
                        break;
                    case -1:
                        $message_body = '<p>'.sprintf( __("Ya se cumplió la fecha de entrega del pedido: %s"), 
                                            '<a href="'.esc_url( $order_url ).'">#'.$order->get_order_number().'</a>'
                                        ) .'</p>';

                        $message = $mailer->wrap_message(
                        // Message head and message body.
                        sprintf( '<h2>'. __( 'Aún no has enviado el pedido %s y ya se venció fecha de entrega. Enviar los pedidos tarde tiene consecuencias.' ) . '</h2>', $order->get_order_number() ), $message_body );

                        // Cliente email, email subject and message.
                        $mailer->send( $vendor_email, sprintf( __( 'Aviso: pedido #%s, se ha vencido el tiempo de entrega' ), $order->get_order_number() ), $message );
                }
            }
        }
    }

It's a bit long but I'm sending a remainder through email to the vendors when there are 3, 2, 1, and 0 days left to the shipping date of their orders.

An order has many sub-orders so I get all the "parent" processing orders and then I loop through each of their product items, then I get the "post_author" of the product to get the vendor and send him an email.

The above code runs daily.

Im using Dokan Multi-vendor plugin.