theMikeD

An excerpt is a (usually) brief, text-only post summary. It is used in various places of a theme when a summary of a post is needed, such as on your blog page and archive pages for terms.
Excerpts are either manually crafted or (usually poorly) automatically extracted from the main post content. Hand crafted ones are better because
<ul>
<li>they avoid things like sentences being cut off in the mid…</li>
<li>they allow you create an actual summary and not just the first x words from the post content</li>
<li>they allow you to do better SEO targeting</li>
<li>they look better</li>
</ul>
This plugin will enforce the use of hand-crafted excerpts by your users by preventing a post without an excerpt from being published.
Classic editor support is based on the work done by Scott Walkinshaw and other contributors, found <a href="https://gist.github.com/swalkinshaw/2695510" rel="nofollow ugc">here</a>.
<h3>Upgrading from a previous version</h3>
Use the upgrade link in the Dashboard (Dashboard > Updates) to upgrade this plugin.
<h3>License and Disclaimer</h3>
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License 2 as published by 
the Free Software Foundation.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
The license for this software can be found here: <a href="http://www.gnu.org/licenses/gpl-2.0.html" rel="nofollow ugc">http://www.gnu.org/licenses/gpl-2.0.html</a>

Mandatory Excerpts for WordPress

Causes the excerpt to be required before a post can be published. Supports both editor types (classic and block aka gutenberg).

Andrew Ozz

Excerpt Editor provides a convenient place for creating and editing all excerpts. It can also add custom excerpts for pages (not possible without a plugin). Features: auto-creating excerpts when publishing new Posts and Pages, displaying customisable excerpts from the content for posts without an excerpt, appending excerpts from the latest posts to each Post or from the sub-pages to each Page, replacing the content for all archive and tags pages with excerpts (eliminates content duplication for SEO).
The excerpts can be used in the RSS feed, displayed on the Home or Archive pages and/or used for meta descriptions. The excerpts can be in any language supported by WordPress and the plugin contains .pot file to facilitate translations.

Excerpt Editor

Quick edit or create excerpts for both Posts and Pages, auto-generate and append excerpts or replace the content with excerpts.

Mandatory Excerpts for WordPress vs Excerpt Editor