tljorgensen

Simple Post Inserter takes various inputs through the settings page and determines three things:
The content you wish to display in your posts, could be plain text, could be some HTML code. 
By default the admin of the site is responsible for any of the content submitted.
The location where the content should be displayed within the post.
Post restrictions. By default if no other setting but the content and location are declared, 
the plugin will insert the content in all of the posts available on the site. This may not be what you 
desire, but you can filter by post type, category, and ID.
Currently the only parameter for placement inside the posts is based off of total paragraphs in a post. 
This will likely change in a future update to something a little more sensible such as: lines of text or character counts.

Simple Post Inserter

Simple post inserter does what it sounds like. Insert some content into a post at your desired location.

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.

Simple Post Inserter vs Insert Blocks Before or After Posts Content