Semantic way of adding an advertisement inside the <main> element?

I am planning to insert an advertisement in the middle of the page content while not breaking accessibility and semantics. My page has its contents inside a <main> element, but I am confused if I should use an <aside> or <div role="complementary"> to nest the advertisement.

What confuses me more is that W3C's documentation says:

complementary: Any section of the document that supports the main content, yet is separate and meaningful on its own.

and in Example 1 below the page, it shows:

<div id="rightsideadvert" role="complementary"> advertisement here...</div>

My understanding is that not all advertisements (like Google Ads) would support or relate to the main content. What is the appropriate markup to use?

<!doctype html>
<html lang='en'>
<meta charset='utf-8' />
<title>Test page</title>
<meta name='viewport' content='width=device-width, initial-scale=1.0' />

<!-- main content -->

<!-- advertisement -->

<!-- main content continues -->