It can still affect the desktop even if you don’t see it on mobile because your site has a separate element for its mobile header, hence, uses an entirely different hook.
To solve the issue, it’s likely a hook unless the theme files are manually edited where that string was typed in manually.
Kindly check the site’s PHP snippets and/or GP elements 1 by 1 to see which one is adding it. 😀
If you can provide us temporary backend access, we can help you search for it.
You can use the private information text field to provide the details. 😀