Metadata
In the App Router you set page metadata by exporting a metadata object or a generateMetadata function from a layout or page.
The App Router has a Metadata API. You export a static metadata object for fixed tags or a generateMetadata function for dynamic ones. Next.js renders the tags into the document head for you. You do not use next/head in the App Router.
Related claims
contradicts
To set the page title in the App Router render a Head element from next/head inside your component.
One says use the Metadata API in the App Router while the other says render next/head there. next/head has no effect in a Server Component so the Metadata API is correct.
supersedesIn the Pages Router you add elements to the document head with next/head.
The App Router Metadata API replaced next/head as the recommended way to set head tags. next/head still applies inside the Pages Router only.