I only put Flash in that category because of the Arrowverse. At the very least, people know these shows exist, whether they watch them or not.
They may not know everything there is to know about Barry’s father in prison because of a time traveling speedster, etc. etc. but at the very least they probably know that the Flash has a lightning bolt logo, wears red, and is fast.
They know that Aquaman is some aquatic superhero (that much can just be inferred from the name), possibly that he’s from Atlantis, and possibly that he talks to fish and is a lame superhero if they’ve listened to any stand-up comedians throughout the ’90s.
I basically use the ‘parent test’ on judging this stuff, personally. If my parents know who or what something is (especially my father), then I consider it more common knowledge than exclusive geek nerd knowledge. Most of my exposure to comic characters when I was growing up and living under their roof were through non-comic media, whether that was cartoons, videogames, or trading cards. I had never read Aquaman comics or anything, and I think I learned everything about him through commercials for the Super Friends cartoon reruns.
But, I’m also of the opinion that there are specific types of people who are going to watch a superhero movie, and these people have some vague notion/interest in superheroes. I don’t think DC (or anyone) is trying to lure in people who aren’t interested in superheroes at this point. I know plenty of people who actively dislike the genre and avoid them (similar to the people who brag that they’ve never seen a Star Wars film in their entire life.)