With the message “Video is not the main content of the page” in the Google Search Console, Google wants to inform you if the Google bot finds a video on the page during crawling, but the video is not integrated “above the fold”. What this means and why it could be important is explained in this article.
The message is not an error message, but serves webmasters as a hint to optimize a page for the Google video search.
Above the fold
“In web design, above the fold refers to the part of a web page that is visible without the user having to scroll.” Source: https://de.wikipedia.org/w/index.php?title=Above_the_fold&oldid=231793859
This means that content is “above the fold” if it is located at the top of the page. This part is also called the “Hero area” on landing pages.
Google video search
Google has introduced video search to be able to search for videos on websites. However, only the videos that represent the main content of the page are listed in the search. Google calls this “above the fold” or in the upper part of the website.