QUOTE: “Supplementary Content contributes to a good user experience on the page, but does not directly help the page achieve it purpose. SC is controlled by webmasters and is an important part of the user experience. One common type of SC is navigation links that allow users to visit other parts of the website. Note that in some cases, content behind tabs may be considered part of the SC of the page. Sometimes the easiest way to identify SC is to look for the parts of the page that are not MC or Ads. ” Google Search Quality Evaluator Guidelines 2019
In Chapter 2, we learned about SERP features. That background is going to help us understand how searchers want to consume information for a particular keyword. The format in which Google chooses to display search results depends on intent, and every query has a unique one. Google describes these intents in their Quality Rater Guidelines as either “know” (find information), “do” (accomplish a goal), “website” (find a specific website), or “visit-in-person” (visit a local business).
The world is mobile today. Most people are searching on Google using a mobile device. The desktop version of a site might be difficult to view and use on a mobile device. As a result, having a mobile ready site is critical to your online presence. In fact, starting in late 2016, Google has begun experiments to primarily use the mobile version of a site's content42 for ranking, parsing structured data, and generating snippets.
Provide full functionality on all devices. Mobile users expect the same functionality - such as commenting and check-out - and content on mobile as well as on all other devices that your website supports. In addition to textual content, make sure that all important images and videos are embedded and accessible on mobile devices. For search engines, provide all structured data and other metadata - such as titles, descriptions, link-elements, and other meta-tags - on all versions of the pages.

QUOTE: “Important: The Lowest rating is appropriate if all or almost all of the MC (main content) on the page is copied with little or no time, effort, expertise, manual curation, or added value for users. Such pages should be rated Lowest, even if the page assigns credit for the content to another source.” – Google Search Quality Evaluator Guidelines 2019
Advertising with Google won't have any effect on your site's presence in our search results. Google never accepts money to include or rank sites in our search results, and it costs nothing to appear in our organic search results. Free resources such as Search Console, the official Webmaster Central blog, and our discussion forum can provide you with a great deal of information about how to optimize your site for organic search.