Insert Specific Page content at the bottom of a post W/O a plugin

Hello and thanks for your help in advance.

Goal: Add the entire content of a specific page (that is already made) to the bottom of specific posts, but not all posts.

I’ve used the “bottom of every post” plugin and it doesn’t do what I want as it: 1) puts the content at the bottom of every post and I only want a few, and 2) it consolidates the text instead of keeping it separated as paragraphs as it is on the actual page.

I know there are other plugins, but I’d rather find out if any of you pros out there (Read: a fun challenge) know a code or script I can insert at the bottom of a post’s HTML that will insert the page [content] I want.

I prefer not to use a plugin for (3) reasons:
1) Updates can break or mess with your site.
2) The author could abandon the plugin, leaving one screwed.
3) Plugins can conflict with each other or affect site load times.

I found the code below in a 5 year old post, but wouldn’t know where to paste it or if is still valid given the number of changes in the last 5 years.

<—–START CODE——>
<?php
$post_id = 12;
$queried_post = get_post($post_id);
?>
<h2><?php echo $queried_post->post_title; ?></h2>
<?php echo $queried_post->post_content; ?>

You have to change the $post_id number to the post you want to use.
<—–END CODE——>

For reference purposes, the page I want to insert into posts is here: https://blog.superstaruniversity.com/chance

Any help or direction would be greatly appreciated.

Thanks,
Alex