I watch very little TV or movies (I find movies particularly attention-demanding, and I need to pause them frequently if I watch them), and tend to prefer less mainstream music styles so there's a lot of shows/movies/music from pop culture that I have never watched or listened. For example I've never watched anything from Game of Thrones, to name one, nor seen any Marvel superhero movie. And as a kid I used to be a Star Wars fan, but that died out quickly and by the time the latest trilogy was filmed I had no interest in it - I eventually watched Episode 7 on TV a few years ago, but found it incredibly uninteresting and haven't had any intention to watch the newer films. About video games, I don't really play that much and typically only a few series or games that I really enjoy (the last few months it's been mostly Civilization and OpenTTD), so for example I never played any Assassin's Creed game (to name a big franchise), nor Fortnite, PUBG, League of Legends, or other multiplayer titles.
Recently I started forcing myself to watch some more culturally significant movies, in particular keeping up with the classics of Italian cinema from the 40s to the 60s, but I've only watched a few of them so far, even if I'd like to continue. The same goes for music, where I try to listen to classics from genres I don't usually listen to a lot - blues, early rock'n'roll, also some jazz even if, not being used to it, I usually take some time and a few listens to appreciate a record.
About To Kill a Mockingbird, I have read it out of personal interest, but I think that outside of the USA it's just another foreign classic, so it's not uncommon to find people who haven't read it. But here in Italy the equivalent "mandatory high school book" is The Betrothed by Alessandro Manzoni, which in fact I have not read (outside of some excerpts), as our teacher that year had us read Il Gattopardo by Giuseppe Tomasi di Lampedusa instead. Which, by the way, 15-year-old me didn't like at all, but after reading more critics and viewpoints I plan to read it again someday. The problem is that, even if I read a lot, I keep buying books faster than I read them...