Delivery date in order email template - Magento 2.4.3-p2

Question

Previously, we used the following module to load the email variable with a custom CreatedAt value. Because this is deprecated, it will not work anymore (https://devdocs.magento.com/guides/v2.4/frontend-dev-guide/templates/template-email-migration.html).

How can we modify the following, to keep using this custom CreatedAt from Magento 2.4.3-p2?

app/code/Mago/Delivery/registration.php

<?php
\Magento\Framework\Component\ComponentRegistrar::register(
\Magento\Framework\Component\ComponentRegistrar::MODULE,
'Mago_Delivery',
__DIR__
);

app/code/Mago/Delivery/etc/module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Mago_Delivery" setup_version="1.0.1">
   </module>
</config>

app/code/Mago/Delivery/etc/di.xml

<?xml version="1.0"?>
<config>
    <preference for="Magento\Sales\Model\Order" type="Mago\Delivery\Model\Rewrite\Order" />
</config>

app/code/Mago/Delivery/Model/Rewrite/Order.php

<?php

namespace Mago\Delivery\Model\Rewrite;

class Order extends \Magento\Sales\Model\Order
{

    public function getDeliveryDate()
    {
        $orderDate = $this->getCreatedAt(); //ORDER CREATED DATE
        return date('Y-m-d', strtotime($orderDate. ' + 10 days'));
    }

}

Finally in your email template you can get this date by:

{{var order.getDeliveryDate()}}

EDIT, new code with Order, Invoice and Creditmemo:

<?php
declare(strict_types=1);

namespace Acme\SalesEmail\Observer\Email;

use Magento\Framework\DataObject;
use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\Locale\ResolverInterface;
use Magento\Framework\Stdlib\DateTime\TimezoneInterface;
use Magento\Sales\Model\Order;
use Magento\Sales\Model\Order\Invoice;
use Magento\Sales\Model\Order\Creditmemo;

class OrderSetTemplateVarsBefore implements ObserverInterface
{
    protected TimezoneInterface $timezone;
    protected string            $locale;

    public function __construct(
        TimezoneInterface $timezone,
        ResolverInterface $localeResolver
    ) {
        $this->timezone = $timezone;
        $this->locale   = $localeResolver->getLocale();
    }

    /**
     * @inheritDoc
     */
    public function execute(Observer $observer): void
    {
        /** @var DataObject $transport */
        $transport = $observer->getEvent()->getData('transportObject');
        /** @var Order $order */
        $order     = $transport->getData('order');
        $orderData = $transport->getData('order_data');        
        /** @var Invoice $invoice */
        $invoice    = $transport->getData('invoice');
        $invoiceData = $transport->getData('invoice_data');
        /** @var Creditmemo $creditmemo */
        $creditmemo    = $transport->getData('creditmemo');
        $creditmemoData = $transport->getData('creditmemo_data');        

        $orderDate = new \DateTime($order->getCreatedAt(), new \DateTimeZone('UTC'));
        $orderData['order_date'] = $this->timezone->formatDateTime(
            $orderDate,
            \IntlDateFormatter::SHORT,
            \IntlDateFormatter::NONE,
            $this->locale
        );
        $transport->setData('order_data', $orderData);
        
        if($invoice){     
            $invoiceDate = new \DateTime($invoice->getCreatedAt(), new \DateTimeZone('UTC'));
            $invoiceData['invoice_date'] = $this->timezone->formatDateTime(
                $invoiceDate,
                \IntlDateFormatter::SHORT,
                \IntlDateFormatter::NONE,
                $this->locale
            );
            $transport->setData('invoice_data', $invoiceData);
        }
        
        if($creditmemo){     
            $creditmemoDate = new \DateTime($creditmemo->getCreatedAt(), new \DateTimeZone('UTC'));
            $creditmemoData['creditmemo_date'] = $this->timezone->formatDateTime(
                $creditmemoDate,
                \IntlDateFormatter::SHORT,
                \IntlDateFormatter::NONE,
                $this->locale
            );
            $transport->setData('creditmemo_data', $creditmemoData);
        }
    }
}

Answer 1

You should use the same logic described in comment https://magento.stackexchange.com/a/358427/91782

I don't recommend to rewrite models such Order just for get some value for email template.

You need to create observer for event email_order_set_template_vars_before, or you can use the same observer for prepare any required data and using transportObject add custom variables to order_data.

You can use order object from transportObject as current order

You also can cover following events (if needed):

• email_order_comment_set_template_vars_before
• email_invoice_set_template_vars_before
• email_invoice_comment_set_template_vars_before
• email_shipment_set_template_vars_before
• email_shipment_comment_set_template_vars_before
• email_creditmemo_set_template_vars_before
• email_creditmemo_comment_set_template_vars_before

You can use single observer for all events because all of them are has order instance and order_data which you can extend for templates.

[Update]

It's easy to create separate module (extension) and you already provided an example in your answer, but I will repeat

1. Create Registration module file

app/code/Acme/SalesEmail/registration.php

<?php
declare(strict_types=1);

use Magento\Framework\Component\ComponentRegistrar;

ComponentRegistrar::register(ComponentRegistrar::MODULE, 'Acme_SalesEmail', __DIR__);

Where Acme is your vendor name and SalesEmail is module name

2. Define module and dependencies

app/code/Acme/SalesEmail/etc/module.xml

<?xml version="1.0" ?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Acme_SalesEmail">
        <sequence>
            <module name="Magento_Sales"/>
        </sequence>
    </module>
</config>

3. Register observers to events

app/code/Acme/SalesEmail/etc/events.xml

<?xml version="1.0" ?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="email_order_set_template_vars_before">
        <observer name="acme_salesemail_observer_email_order_set_template_vars_before"
                  instance="Acme\SalesEmail\Observer\Email\OrderSetTemplateVarsBefore"/>
    </event>
    <event name="email_order_comment_set_template_vars_before">
        <observer name="acme_salesemail_observer_email_order_comment_set_template_vars_before"
                  instance="Acme\SalesEmail\Observer\Email\OrderSetTemplateVarsBefore"/>
    </event>
    <event name="email_invoice_set_template_vars_before">
        <observer name="acme_salesemail_observer_email_invoice_set_template_vars_before"
                  instance="Acme\SalesEmail\Observer\Email\OrderSetTemplateVarsBefore"/>
    </event>
    <event name="email_invoice_comment_set_template_vars_before">
        <observer name="acme_salesemail_observer_email_invoice_comment_set_template_vars_before"
                  instance="Acme\SalesEmail\Observer\Email\OrderSetTemplateVarsBefore"/>
    </event>
    <event name="email_shipment_set_template_vars_before">
        <observer name="acme_salesemail_observer_email_shipment_set_template_vars_before"
                  instance="Acme\SalesEmail\Observer\Email\OrderSetTemplateVarsBefore"/>
    </event>
    <event name="email_shipment_comment_set_template_vars_before">
        <observer name="acme_salesemail_observer_email_shipment_comment_set_template_vars_before"
                  instance="Acme\SalesEmail\Observer\Email\OrderSetTemplateVarsBefore"/>
    </event>
    <event name="email_creditmemo_set_template_vars_before">
        <observer name="acme_salesemail_observer_email_creditmemo_set_template_vars_before"
                  instance="Acme\SalesEmail\Observer\Email\OrderSetTemplateVarsBefore"/>
    </event>
    <event name="email_creditmemo_comment_set_template_vars_before">
        <observer name="acme_salesemail_observer_email_creditmemo_comment_set_template_vars_before"
                  instance="Acme\SalesEmail\Observer\Email\OrderSetTemplateVarsBefore"/>
    </event>
</config>

4. Create universal observer

app/code/Acme/SalesEmail/Observer/Email/OrderSetTemplateVarsBefore.php

<?php
declare(strict_types=1);

namespace Acme\SalesEmail\Observer\Email;

use Magento\Framework\DataObject;
use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Framework\Locale\ResolverInterface;
use Magento\Framework\Stdlib\DateTime\TimezoneInterface;
use Magento\Sales\Model\Order;

class OrderSetTemplateVarsBefore implements ObserverInterface
{
    protected TimezoneInterface $timezone;
    protected string            $locale;

    public function __construct(
        TimezoneInterface $timezone,
        ResolverInterface $localeResolver
    ) {
        $this->timezone = $timezone;
        $this->locale   = $localeResolver->getLocale();
    }

    /**
     * @inheritDoc
     */
    public function execute(Observer $observer): void
    {
        /** @var DataObject $transport */
        $transport = $observer->getEvent()->getData('transportObject');
        /** @var Order $order */
        $order     = $transport->getData('order');
        $orderData = $transport->getData('order_data');

        $billing   = $order->getBillingAddress();
        $orderData['customer_firstname'] = $billing->getFirstname();
        $orderData['customer_lastname']  = $billing->getLastname();

        $deliveryDate = new \DateTime($order->getCreatedAt(), new \DateTimeZone('UTC'));
        $deliveryDate->add(new \DateInterval('P10D'));

        $orderData['delivery_date'] = $this->timezone->formatDateTime(
            $deliveryDate,
            \IntlDateFormatter::SHORT,
            \IntlDateFormatter::NONE,
            $this->locale
        );

        $transport->setData('order_data', $orderData);
    }
}

P.S.

You can use Generator Tool for create some skeleton of code