Without an H1, search engines and screen readers have no main heading to tell them what the page is about.
Why Joomla sites get it
In Joomla the H1 on an article page is normally the title, printed by the template, not something in the article text. It goes missing when Show Title is set to Hide (in the article’s Options, the menu item or the Articles options) and nothing else provides an H1, or when a template or override prints the title in a smaller heading. Because the H1 comes from the template, you can’t see the problem by reading the article text.
Fix it by hand
- View the page and check its headings, for example with your browser’s developer tools.
- If the title is hidden, set Show Title to Show, or turn on the menu item’s Show Page Heading.
- If you want the title hidden, make the first heading in the article text an H1 instead.
Fix it with MetaGen
MetaGen’s site scan fetches each published article as a visitor sees it and checks for an H1. The H1 missing row lists the pages without one, with a link to edit each article. Run the scan with Scan site, or switch on the MetaGen – site scan scheduled task to rescan weekly.
MetaGen is free for Joomla 5 and 6. See all the SEO warnings MetaGen checks.