I have a personal website built with jekyll and hosted on Github pages. I am trying to add a sub-site blog within the same domain. For this, I set up a blog.md page and followed the instructions from this website: https://www.garron.me/en/blog/multi-blog-site-jekyll.html. The idea is that if I access http://<mydomain>.com it will go to my personal website, and if I go to http://<mydomain>.com/blog it will go to a different site also set up with jekyll.
My file structure is different than what they suggest in the link above. It is like this:
/personalwebsite
config.yml
index.md
(other personal website pages).md
blog.md
/_site
/_layouts
/_posts
My index.md page is completely customized, and I wrote my own layout for that website. It is a static site and everything in _posts is ignored by it. My blog.md page is also on the root folder and it changes according to _config.yml. I am trying to use Github jekyll themes for it. The theme loads, but instead of showing the posts, it shows the code:

This is what blog.md looks like:
---
layout: blog
title: the blog
permalink: blog
---
{% raw %}
{% for post in site.posts %}
{% if post.categories contains 'blog' %}
<div class="post">
<h3 class="title"><a href="{{ post.url }}">{{ post.title }}</a></h3>
<p class="meta">Date: {{ post.date }}</p>
<div class="entry">
{{ post.content | strip_html | truncatewords: 100 }}
</div>
</div>
{% endif %}
{% endfor %}
{% endraw %}
And this is what a post looks like:
---
layout: post
title: New test
category: blog
---
This is a test post
If I remove the {% raw %} parts in blog.md, the posts show up like this:

I have already checked that my posts are in the right place, the category parameter is filled in, the dates and post filenames are properly formatted. What am I doing wrong? Jekyll does not show any error messages other than a Github metadata warning:
GitHub Metadata: No GitHub API authentication could be found. Some fields may be missing or have incorrect data