You don’t have to be a hacker if someone else does the hacking for you. I literally just now googled “OnlyFans content downloader” and the first result was from Google App Store with a free program that says it can download any content from OnlyFans for free and currently has a 4 out of 5 star rating as rated by over 70,000 users.Maybe a hacker might have some success but for regular joes doing it they've made it pretty imprenetable. Apparently you can still screenshot but you just get a black screen.
Even with that aside, a website cant stop people taking screenshots. Ever. They can make it so you can’t right click and save an image, or they could even try and disable the print screen button on your keyboard (though I don’t see how that would work) and can do the same with phones but there aren’t any impenetrable ways to stop people getting screenshots of anything. The internet is a public place.