Override the vendor/magento/module-sales/view/frontend/templates/email/items/order/default.phtml file on your theme and add the below code.
<?php
/**
* Copyright © Magento, Inc. All rights reserved.
* See COPYING.txt for license details.
*/
// phpcs:disable Magento2.Templates.ThisInTemplate
/** @var $block MagentoSalesBlockOrderEmailItemsDefaultItems */
/** @var $_item MagentoSalesModelOrderItem */
$_item = $block->getItem();
$_order = $_item->getOrder();
$objectManager = MagentoFrameworkAppObjectManager::getInstance();
$product_id = $_item->getProduct()->getId();
$product = $objectManager->create('MagentoCatalogModelProduct')->load($product_id);
$optionId = $product->getCustomAttr();
$optionText = '';
$attr = $product->getResource()->getAttribute('custom_attr');
if ($attr->usesSource()) {
$optionText = $attr->getSource()->getOptionText($optionId);
}
?>
<tr>
<td class="item-info<?= ($block->getItemOptions() ? ' has-extra' : '') ?>">
<p class="product-name"><?= $block->escapeHtml($_item->getName()) ?></p>
<p class="sku" style="font-size: 11px;"><strong><?=$block->escapeHtml(__('SKU')) ?>:</strong><?=$block->escapeHtml($block->getSku($_item)) ?></p>
<p class="description" style="font-size: 11px;"><strong><?=$block->escapeHtml(__('Description')) ?>:</strong><?php echo $product->getShortDescription(); ?></p>
<?php if($optionText){ ?>
<p class="custom-attr" style="font-size: 11px;"><strong><?=$block->escapeHtml(__('Custom Attribute')) ?>:</strong><?=$block->escapeHtml($optionText) ?></p>
<?php } ?>
<?php if ($block->getItemOptions()) : ?>
<dl class="item-options">
<?php foreach ($block->getItemOptions() as $option) : ?>
<dt><strong><em><?= $block->escapeHtml($option['label']) ?></em></strong></dt>
<dd>
<?= /* @noEscape */ nl2br($block->escapeHtml($option['value'])) ?>
</dd>
<?php endforeach; ?>
</dl>
<?php endif; ?>
<?php $addInfoBlock = $block->getProductAdditionalInformationBlock(); ?>
<?php if ($addInfoBlock) :?>
<?= $addInfoBlock->setItem($_item)->toHtml() ?>
<?php endif; ?>
<?= $block->escapeHtml($_item->getDescription()) ?>
</td>
<td class="item-qty"><?= (float) $_item->getQtyOrdered() ?></td>
<td class="item-price">
<?= /* @noEscape */ $block->getItemPrice($_item) ?>
</td>
</tr>
<?php if ($_item->getGiftMessageId()
&& $_giftMessage = $this->helper(MagentoGiftMessageHelperMessage::class)
->getGiftMessage($_item->getGiftMessageId())
) : ?>
<tr>
<td colspan="3" class="item-extra">
<table class="message-gift">
<tr>
<td>
<h3><?= $block->escapeHtml(__('Gift Message')) ?></h3>
<strong><?= $block->escapeHtml(__('From:')) ?></strong> <?= $block->escapeHtml($_giftMessage->getSender()) ?>
<br /><strong><?= $block->escapeHtml(__('To:')) ?></strong> <?= $block->escapeHtml($_giftMessage->getRecipient()) ?>
<br /><strong><?= $block->escapeHtml(__('Message:')) ?></strong>
<br /><?= $block->escapeHtml($_giftMessage->getMessage()) ?>
</td>
</tr>
</table>
</td>
</tr>
<?php endif; ?>
