Author: admin

File vendor/magento/module-checkout/Controller/Onepage/Success.php

Should look like:

public function execute()
    {
        $session = $this->getOnepage()->getCheckout();
        $session
            ->setLastOrderId(OLD_ID)
            ->setLastRealOrderId('OLD INCREMENT ID')
            ->setLastOrderStatus('Pending');

Edit file vendor/magento/framework/DB/Statement/Pdo/Mysql.php

            return $this->tryExecute(function () use ($params) {
                $writer = new \Zend_Log_Writer_Stream(BP . '/var/log/debugSql.log');
                $logger = new \Zend_Log();
                $logger->addWriter($writer);
                $logger->debug($this->_stmt->queryString);
                $logger->debug(json_encode($params));
                $logger->debug('================');
                return $params !== null ? $this->_stmt->execute($params) : $this->_stmt->execute();
            });

By help of a script you can send Shipment, Creditmemo etc emails how much you want

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

use Magento\Framework\App\Bootstrap;

require 'app/bootstrap.php';

$bootstrap = Bootstrap::create(BP, $_SERVER);
$objectManager = $bootstrap->getObjectManager();
$state = $objectManager->get(Magento\Framework\App\State::class);
$state->setAreaCode(\Magento\Framework\App\Area::AREA_FRONTEND);
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();

/** @var Magento\Store\Model\App\Emulation $emulation */
$emulation = $objectManager->create('Magento\Store\Model\App\Emulation');
$emulation->startEnvironmentEmulation(1, \Magento\Framework\App\Area::AREA_FRONTEND, true);


/** @var \Magento\Sales\Model\ResourceModel\Order\Creditmemo\Collection $shipmentCollection */
$collection = $objectManager->get(\Magento\Sales\Model\ResourceModel\Order\Creditmemo\Collection::class);
/** @var Magento\Sales\Model\Order\Creditmemo $subject */
$subject = $collection->getLastItem();


/** @var Magento\Sales\Model\Order\Email\Sender\CreditmemoSender $sender */
$sender = $objectManager->get(Magento\Sales\Model\Order\Email\Sender\CreditmemoSender::class);
$sender->send($subject);


$emulation->stopEnvironmentEmulation();
echo "Done";

\Magento\Framework\App\ObjectManager::getInstance()
    ->get(\Psr\Log\LoggerInterface::class)->debug('message');

For custom .log file:

                $writer = new \Zend_Log_Writer_Stream(BP . '/var/log/debugSql.log');
                $logger = new \Zend_Log();
                $logger->addWriter($writer);