I'm not sure what you're asking.
Figure from W3Schools
In addition to what Jon and Nancy have said, I am glad that the article that Nancy referred to - https://www.w3schools.com/html/html5_semantic_elements.asp - does expand on the use of headers and footers. These are not only used in the main document, but can also be used in other elements that require a header.
Having said that, in my personal opinion, an outline of the document is the most important goal for SEO and screen readers. This is where header tags play an important role. As an example, have a look at
What this tells me is that both the body and the nav elements have no heading (hx).