Dmitry

You don’t need to install an additional plugin. Just add this code snippet to your theme’s functions.php file and everything will work.

Search bots do not see this link. It is displayed only in the user’s browser.
If you want to remove this, then try adding this code to the functions.php file:
add_filter( 'slim_seo_sitemap_style', '__return_false' );

This will remove the sitemap styling.

1. The mu-plugins folder in WordPress is for adding special plugins called must-use plugins. The mu-plugins folder is not included in the default WordPress installation. If you want to use must-use plugins, you need to create this folder manually inside the wp-content folder. Once the mu-plugins folder is created, you can add PHP files with plugin code to it and they will be automatically activated.

2. You can name the file with any name, for example aggregate-rating.php
When the files are found in the mu-plugins directory, WordPress will automatically enable these files. This means that the code in these files is executed every time WordPress is loaded. Plugins such as The SEO Framework can then use this code if it provides features or hooks that the plugin expects to see.

3. For example, if you create a new PHP file in the mu-plugins folder with whatever name you want (e.g. aggregate-rating.php) and add the code to it:

<?php
function my_custom_schema( $data, $context ) {

    if (is_single(10)) {
		$data[] = [
			"@type" => "AggregateRating",
			"ratingValue" => "88",
			"bestRating" => "100",
			"ratingCount" => "20",
		];
		return $data;
	}
	elseif is_single(11)) {
		$data[] = [
			"@type" => "AggregateRating",
			"ratingValue" => "95",
			"bestRating" => "100",
			"ratingCount" => "25",
		];
		return $data;
	}
	elseif is_single(12)) {
		$data[] = [
			"@type" => "AggregateRating",
			"ratingValue" => "96",
			"bestRating" => "100",
			"ratingCount" => "24",
		];
		return $data;
	}
	else {
		return $data;
	}
}
add_filter( 'the_seo_framework_schema_graph_data', 'my_custom_schema', 10, 2);

then he AggregateRating markup will appear at the end of the graph array on article pages with IDs 10, 11 12.
Post IDs can be viewed on the /wp-admin/edit.php page and in the list of all entries, hover your mouse over the title of the post for which you want to find out the ID. A line on a gray background will appear at the bottom of the screen showing the ID of that post (post=id). The post ID is the number that comes right after the posts= parameter.
This way you can add any markup with different properties and values for each post with a specific ID.

The list of markups that are supported by Google Search can be found here: https://developers.google.com/search/docs/appearance/structured-data/search-gallery
You can test the markup on this page: https://search.google.com/test/rich-results

Structured data is powerful, but you must follow Google’s strict policies in order to be eligible for this. If you fail to comply, they’ll flag your website for spam.

Why doesn’t TSF add a link tag with the canonical post URL on page_comments pages?
Here’s what it looks like for other SEO plugins:

Yoast:

<meta name='robots' content='index, follow, max-image-preview:large, max-snippet:-1, max-video-preview:-1' />
<link rel="canonical" href="https://example.com/hello-world/">

—
Rank Math:

<meta name="robots" content="follow, index, max-snippet:-1, max-video-preview:-1, max-image-preview:large"/>
<link rel="canonical" href="https://example.com/hello-world/" />

—
AIOSEO:

<meta name="robots" content="noindex, nofollow, max-image-preview:large" />
<link rel="canonical" href="https://example.com/hello-world/" />

—
SEOPress:

<meta name="robots" content="index, follow">
<meta name="googlebot" content="index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1">
<meta name="bingbot" content="index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1">
<link rel="canonical" href="https://example.com/hello-world/">

—
Squirrly SEO:

<meta name="robots" content="index,follow">
<meta name="googlebot" content="index,follow,max-snippet:-1,max-image-preview:large,max-video-preview:-1">
<meta name="bingbot" content="index,follow,max-snippet:-1,max-image-preview:large,max-video-preview:-1">
<link rel="canonical" href="https://example.com/hello-world/" />

—
Slim SEO:

<meta name='robots' content='max-image-preview:large, max-snippet:-1, max-video-preview:-1' />
<link rel="canonical" href="https://example.com/hello-world/comment-page-1/#comments">

As you can see from the examples above, almost everyone adds a link tag with the canonical URL of the post, with the exception of Slim SEO, which has a comments page instead of a post page. And noindex, nofollow only adds AIOSEO.