HTML in product additional information tab

WooCommerce runs attribute values through a filter to remove real html and show it in a printable format.

The way forward is to retrieve the attribute values direct from the database. You’ll need to make a custom template for product-attributes.php. The copy goes at:
themes/your-child-theme/woocommerce/single-product/product-attributes.php

In the copy, use something like:

$product_id = $product->get_id();
$ats = get_post_meta( $product_id, '_product_attributes', true );
foreach( $ats as $at ) {
  $product_attribute['value'] = html_entity_decode( $at['value'], ENT_COMPAT | ENT_HTML5 );
  }
}

Some PHP skills will be necessary to get it working.

This only works for custom attributes. These are saved with html. However, global attributes are stripped of any html before saving to the database.

WooCommerce strips html as a safety feature. If you are using unfiltered html, be sure it comes from a trusted source.

Ok, thank you, so the product-attributes.php should look like this? Can i just add your code or replace it? In /your-child-theme/woocommerce/single-product/product-attributes.php (I am using twenty twenty theme)

defined( 'ABSPATH' ) || exit;

if ( ! $product_attributes ) {
	return;
}
?>
<table class="woocommerce-product-attributes shop_attributes">
	<?php foreach ( $product_attributes as $product_attribute_key => $product_attribute ) : ?>
		<tr class="woocommerce-product-attributes-item woocommerce-product-attributes-item--<?php echo esc_attr( $product_attribute_key ); ?>">
			<th class="woocommerce-product-attributes-item__label"><?php echo wp_kses_post( $product_attribute['label'] ); ?></th>
			<td class="woocommerce-product-attributes-item__value"><?php echo wp_kses_post( $product_attribute['value'] ); ?></td>
		</tr>
	<?php endforeach; ?>
</table>
$product_id = $product->get_id();
$ats = get_post_meta( $product_id, '_product_attributes', true );
foreach( $ats as $at ) {
  $product_attribute['value'] = html_entity_decode( $at['value'], ENT_COMPAT | ENT_HTML5 );
  }

No, it was meant to be an approach, not exact code. Try this:
https://pastebin.com/Tm8SG9kk

If it doesn’t work for you, please post the address of a relevant product page.

It works perfect, thank you very much!