What the fake iphone 16 update screen is
The update screen has not changed much across recent iPhone generations, which works in your favour: this reads correctly on any modern iPhone rather than only the newest one.
The phrasing here is the preparing stage rather than the installing one — the bit before the restart, which is the longer and more irritating half.
iPhone 16 update prank, no download
Add the page to the home screen and open it from there for a screen with no browser interface at all.
Nothing is installed, no permission is requested, and swiping the page away ends it completely.
How to run it, and how to stop it
Press F for fullscreen, then F11 to hide the browser’s own toolbars. That second step is the one that matters: an address bar sitting above the screen gives the whole thing away instantly.
To end it: Escape leaves fullscreen, F11 brings the toolbars back, and closing the tab removes it entirely. Nothing is installed, no file is written and no setting is changed, so there is nothing to undo afterwards.
Worth saying plainly — use this on people who will find it funny, and on machines you are allowed to touch. Show them the way out once the joke has landed.