Sec,ch,ua,mobile:,?0

: Deliver larger images or background videos that might be too heavy for mobile data connections.

When a server identifies a user as desktop-based via this header, you should deliver:

: It is a "low-entropy" hint, meaning browsers like Chrome send it by default on every secure (HTTPS) request without the server needing to ask for it. sec,ch,ua,mobile:,?0

: It follows the Structured Field Values format, using a question mark followed by a boolean: ?0 : Desktop (False). ?1 : Mobile (True).

For more technical implementation details, you can refer to the official documentation on MDN Web Docs. Sec-CH-UA-Mobile header - HTTP - MDN Web Docs : Deliver larger images or background videos that

: Include interactive elements that rely on mouse-hover actions, which don't exist on touchscreens.

: Serve expansive, multi-column designs rather than single-column mobile stacks. : Serve expansive

The header sec-ch-ua-mobile: ?0 is a that tells a web server the request is coming from a desktop device .