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; ?>