WhizKins

WPSimpleInsert is a plugin to insert custom code in your blog posts. It includes options to either add the code above 
or below post content.
Features:
<ul>
<li>Add custom HTML/PHP/JavaScript to your posts.</li>
<li>Ability to add custom code above or below post content.</li>
<li>Options to hide the code from certain pages like the home page and category and archives pages.</li>
</ul>

WP Simple Insert

A plugin to insert custom HTML or PHP code in your posts. Includes options to insert before or after post content.

Whodunit

Jb Audras

Maxime Pertici

This plugin gives the capability to automatically add content before and/or after your posts, pages, or any public custom post types.
It is also possible to prevent your before/after content from showing on a post or a page directly from the editor screen (works on both Classic Editor and Block Editor). You can also prevent your before/after content from displaying on specific post types or categories.
With this plugin, build your before/after content within the Gutenberg block editor, even if you are using Classic Editor!
Indeed, the block editor is activated for these specific blocks of contents even if Gutenberg is not activated on your website!
I strongly recommend to use it alongside one of my other free plugins, <a href="https://wordpress.org/plugins/reusable-blocks-extended/" rel="ugc">Reusable Blocks Extended</a>. These two plugins are totaly independant, but together they provide a full editorial experience! ⭐️

Insert Blocks Before or After Posts Content

The Blocksy theme gives the opportunity to customize some features before and after the content but prevent you to choose the order of eventual additional content you may try to add in these places. This plugin is pretty cool as you can add all the blocks you need in the order and composition you need.

Very handy

Automatically insert blocks of content before and/or after each posts/page content.

WP Simple Insert vs Insert Blocks Before or After Posts Content