carestad

If your site is depending on posts to have their thumbnail images set, this is the plugin for you. Also makes it possible 
to require tags in every new post.
When trying to save a post without at thumbnail or tags and when activated, the user will get a warning and the post will 
be saved as a draft instead.

Post Requirements

This plugin allows you to require posts to have thumbnail set and/or tags.

Josh Hartman

Tired of uncategorized posts? Use this simple plugin to require users to choose a post category before updating or publishing a post. By default this only applies to normal posts. If you wish to require a category/taxonomy for a custom post type see the FAQ for filter hook usage examples.
<h4>Translators</h4>
<ul>
<li>French (fr_FR) – Dominique V.</li>
<li>Spanish (es_ES) – <a href="http://www.webhostinghub.com" rel="nofollow ugc">Andrew Kurtis – WebHostingHub</a></li>
<li>Polish (pl_PL) – Michał Papliński</li>
<li>Finnish (fi) – Sanapaino</li>
</ul>
If you have created your own language pack, or have an update of an existing one, you can send the <a href="https://codex.wordpress.org/Translating_WordPress" rel="nofollow ugc">PO and MO files</a> to <a href="https://www.warpconduit.net/contact" rel="nofollow ugc">me</a> so that I can bundle it into the plugin. <a href="https://plugins.svn.wordpress.org/require-post-category/trunk/languages/require-post-category.pot" rel="nofollow ugc">Download the latest POT file</a>.

Require Post Category

This plugin is fantastic, and I was very easily able to customize it to work with my custom post types and custom taxonomies. Great work, thanks!

Easy to customize

Simply install the plugin and activate. Works with both classic and block editors. Nice work.

Easy and Effective

Require users to choose a post category before updating or publishing a post.

Post Requirements vs Require Post Category