Georgi Popov

This plugin provides a list of similar / related entries to an article or a custom post type entry.
This list could be added in the form of a:
<ol>
<li>Gutenberg Block</li>
<li>Shortcode</li>
<li>Widget</li>
</ol>
If you add a widget to the sidebar it will only appear when on the details view of an entry, as similarity cannot be calculated when on a list page of multiple entries.
The syntax for the shortcode is <code>[magadanski-similar-posts id="" post_type="" taxonomy="" limit=""]</code>
You can use the attributes as follows:
<ol>
<li>ID — (integer) the ID of the post you’d like to get similar posts for. Default value: the current post ID.</li>
<li>post_type — (string) the post type you’d like to query. Default value: “post”.</li>
<li>taxonomy — (string) the taxonomy based on which you’d like to get similar items. Default value: “category”.</li>
<li>limit — (integer) a maximum number of results you’d like to receive. Default value: 5.</li>
</ol>
The similarity is considered based on the number of common categories (or other taxonomy terms) for this post and the rest of the posts in your blog.

M Similar Posts

This plugin lists similar to the current post based on the number of common categories.

shawfactor

Quickly increase your readers’ engagement by adding related posts to the bottom of your post content.
Posts with the most terms in common will display at the top!
This plugin is capable of finding related posts in multiple taxonomies and post types. Include or exclude terms from the search for related posts. Change the look and feel by using your own templates in your (child) theme.
Additionally this plugin allows you to override the related posts that are automatically generated and choose your own related posts.
Requires wp_body_open
Note this plugin requires wordpress 5.2 and for your theme to support the wp_body_open hook (most good themes do).
Like this plugin? Please consider <a href="https://wordpress.org/support/view/plugin-reviews/lh-related-posts-by-taxonomy/" rel="ugc">leaving a 5-star review</a>.
Love this plugin or want to help the LocalHero Project? Please consider <a href="https://lhero.org/portfolio/lh-related-posts-by-taxonomy/" rel="nofollow ugc">making a donation</a>.
Plugin features:
<ul>
<li>Small Footprint. Unlike many other related post plugins this will have a minimal impact on site speed!</li>
<li>Highly Adjustable layout!</li>
<li>The ability to optionally manually set the related posts for each post in the post edit screen.</li>
</ul>

LH Related Posts by Taxonomy

A lightweight decisions not options related posts plugin.

M Similar Posts vs LH Related Posts by Taxonomy