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.

Tekod lab.

Purpose of 404 page is to inform visitor that WordPress cannot resolve current URL, 
but leaves the visitor wondering why. 
Whether the page was deleted or simply the link was not typed correctly.
This plugin analyzes what is entered in the URL, compares it with all existing urls on the site, finds the closest ones and offers the visitor the 5 closest ones. 
Something like “did you mean…”.
<h3>Usage</h3>
The plugin supports both classic and block themes.
For classic themes, you need to add shortcode to the template of your 404 page:
 
For block themes, you will get a new Gutenberg block “404 page: similar links” that you simply insert into your template.
Finally, the plugin allows you to override template to completely customize resulting HTML, 
and a few filter hooks to modify its logic.
<h3>Contact</h3>
Please, send bug reports and feature requests to <a href="mailto:office@tekod.com" rel="nofollow ugc">office@tekod.com</a>

Suggest 404 links

Appends "did you mean" links to your "404" page.

M Similar Posts vs Suggest 404 links