Hi there,
I do see the product images in the feed:
<description><![CDATA[<a href="https://ventadeactivos.es/producto/promocion-toquero-2b/" title="Promoción Toquero, 2B" rel="nofollow"><img width="150" height="150" src="https://ventadeactivos.es/web/wp-content/uploads/2020/06/PORTADA-150x150.jpg" class="webfeedsFeaturedVisual wp-post-image" alt="" style="display: block; margin: auto; margin-bottom: 5px;max-width: 100%;" link_thumbnail="1" ... /></a>
You can see the IMG and the SRC URL of the image being used.
If you are not seeing the images still, the RSS feed may be cached… you can try adding a cachebuster to the end of your URL, such as “?nocache123” etc, it will treat the feed as a new/different feed, and images may show then.