WordPress’s editor is only a page content editor, not a full-page editor.
While there is a Heading Block, this is for heading text within the content: https://wordpress.org/support/article/heading-block/
WordPress’s editor does not operate outside of page content and therefore cannot modify headers and footers.
There is some full-page editing functionality planned for later, but this won’t be happening any time soon.
James…thank you so much for the clear and fast explanation. It’s sort of what I thought, but just wanted to make sure. Thanks again.