Oh I see! That clears it up! Smart and sneaky eh?That means you run across a 'responsive website'.
The easiest way to tell whether a website is responsive is to resize the browser window on a desktop. If the content changes, then it's a responsive website.
When a website is responsive, even if you 'request desktop version', the phone still can't show the desktop version because the layout of the website is determined by the screen resolution.
(original image link: https://searchengineland.com/figz/wp-content/seloads/2018/04/responsive-design.gif)
The 'request desktop version' only works on websites that actually provide 2 versions (one desktop, one mobile).