Yes this happens all the time and how is modern espionage, for the time being, extensively communicates.
Typically this happens on websites that look like junk/ad websites to you and me. Also sometimes they will look like the ads you see on parked domains.
There will be hidden words, or perhaps you will need to know how to adjust the CSS in chrome developer tools. Often times it is a small URI fragment you need to append to the URL, or a specific place to click every time.
Again I want to emphasize how common this is, and the “dark web” is not used nearly as much in terms of overall volume by such groups.
Owlhousing.com was until recently and still probably is one such site. It looked like some junk casino ad website, but scroll down for a very lengthy period and you would find...sophisticated electronic Microscopes for sale out of Hong Kong. Now it is some car website.
The best way to find these websites is to use Spyse.com. Using the “prefix” search operator enter something like “000000000” or “aaaaaaaaa”. Hundreds if not thousands of sites show up. No real person would take out these domains. Start with them.