在WP主页上显示缩短的帖子摘要

In my WordPress installation, I'm trying to display a short post text summary on the homepage (See attached image and text highlighted in red)

The homepage contains a stacked list of my most recent posts (the default one).

The two common solutions of which I'm already aware:

Solution #1 - The "Insert More" tag:- I don't want to have a "more" button. I simply need to have the featured image, author, categories and then the shortened post summary.

Solution #2 - Replace "the_content" with "the_excerpt" - I've looked for "the_content" inside my index.php and archive.php, and it doesn't seem to exist in those files. It exists in blog.php but changing it to "the_excerpt" does nothing, and there is no option for excerpts when creating a post.

My WP theme is Qreator responsive WP

Thanks in advance for help!

<?php   
  add_filter("the_content", "plugin_myContentFilter");

  function plugin_myContentFilter($content)
  {
    // Take the existing content and return a subset of it
    return substr($content, 0, 300);
  }
?>

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