Suggestion, replace this:

    <item>
      <title>Last Blog Post</title>
      <description>
        I am Jack's XML Parser. I consume unclosed tags I kill jack.
      </description>
      <link>https://xsltblogdemo.vgr.land/content/posts/20250707.xml</link>
      <guid isPermaLink="false">post-20250707</guid>
      <pubDate>Mon, 7 Jul 2025 13:00:00 +0000</pubDate>
      <author>vgr.xsltbf@example.com (vgr)</author>
    </item>

    <post
      title="Last Blog Post"
      description="I am Jack's XML Parser. I consume unclosed tags I kill jack."
      link="https://xsltblogdemo.vgr.land/content/posts/20250707.xml"
      isPermaLink="false"
      guid="post-20250707"
      pubDate="Mon, 7 Jul 2025 13:00:00 +0000"
      author="vgr.xsltbf@example.com (vgr)">
    Content of the post....
    </post>

Perfectly illustrating one of XML's stupidest flaws.

I don't know if this is intentionally hilarious or unintentionally hilarious, I guess it's the same result either way.