Click "Download all sizes" (A)

That's not visible here. Do you have any gadgets/user scripts activated?

But I especially used an incognito window to view the page.
The HTML is

<div class="stockphoto-layout-vertical" ... <span class="stockphoto_buttonrow" 
title="Download all sizes" .... ><a>Download</a><small>all sizes<

Anyway it is not me who installed the stockphoto gadget, because I was using an incognito window.

There are infinite sizes, so 'all sizes' doesn't exist to begin with.

This whole gadget that Commons uses is very outdated in many ways (for instance, those links in the gadget PRE DATE the list on the normal file page. So the whole option isn't as useful as it was when originally designed.)