Not even fiction, necessarily. I went for "content" (which was probably a poor choice of words), and I meant it in the most general form possible. All media that you consume, be it fiction, non-fiction, or even what I've written here, I think, is subject to the idea of "intellectual heaviness". All media have ideas that are presented, and by virtue of it being presented, to be digested, filtered through the lens of what you believe. Everything has a story to tell, and everyone has their own ideas of what those stories mean to them. Perhaps that's me trying to find meaning in the ultimately-meaningless, and you're free to think and express that.
Also, I'd disagree with the idea that fiction has a weak effect on people. Fiction, I think, is stronger than non-fiction in this regard. A good story can fundamentally alter how someone thinks, especially at a young age.
The "I'm not like other girls" thing (which while sorta dead in our and older generations, is very much alive in Zoomers), for instance, is perpetuated by the idea that women have to be a certain way, as well as the glorification/idolization of women who are "different" in media. There's a pressure on girls to be "girly", but then another, sometimes stronger pressure that tells them that they should be "different" from that ideal. That's sorta the crux of the issue. The way to be "different", it seems, is to go against the "girly" stereotype. But it's also "bad" to not be "girly", so you have to "justify" it by putting down other girls who are "not different", by being not "girly" and telling the other girls that they are "girly" and therefore "not different".
Now, that's coming from me, an assigned male from birth enby, so I think the message may have gotten a little mangled there. But I'm hoping you get the point. All media can influence people. Of course, as you age and become wiser, it's usually harder to be influenced by such media, especially if it contradicts your beliefs or your identity. That's part of what I call "intellectual heaviness". Of course, it's entirely possible to 100% agree with a piece of media, but it's hard to digest because it's not something you've considered at all before, hence, "part".