It is easy to see that H1 tags are important for SEO, particularly regarding usability and accessibility, so ideally there should be one on each page of a website. Google has previously said there can be more than one, but it makes sense to just use a single H1 and use the other headings in a hierarchal way, otherwise you can cause unnecessary confusion to both search engines and users.
Regardless of what John Mueller has said recently, headings still have a use in SEO when used correctly. It’s a complex task for search engines to read the context of a page, so they use data from different factors, including the page title and H1 tags. Reading the HTML code, Google can help identify the page content and know whether it is relevant to a search based on the information in the title and H1 tags. And sometimes, H1s are used in place of a title tag in SERPs, so it makes sense to include the topic of the page, so you still have a good headline.
Headings help improve a page’s usability as they make it easier for users to navigate. A glance at the H1 tag will indicate what the page is about, and the following headings provide users with an idea on how the page progresses. It’s a little like chapters in a book (giving you a good idea of how the story develops) but you don’t want to have long headings as it’s better to keep them short and to the point.