So, here’s a thought:
The types of fandom that are most often considered traditional and acceptable, and which are often either male-dominated or coded as masculine, tend to be acquisitive, whether in terms of knowledge (obscure trivia) or merchandise (collectibles). Whereas, by contrast, the types of fandom most often considered insincere, non-serious or “unreal”, and which are often either female-dominated or coded as feminine , tend to be creative, such as making costumes, writing fanfic and drawing fanart.
Which is arguably an interesting expression of gender dynamics within fandom, in the sense of being a direct response to gender representation within the canon of particular franchises: namely, that because men, and particularly straight white cismen, are so ubiquitous within popular narrative(s), they have less need to create personal fan interpretations in order to see themselves represented, or to correct/ameliorate stereotypical portrayals; whereas women - and, indeed, members of any other group likely to suffer from poor representation - do.
Which isn’t to say that it’s impossible to be both an acquisitive and a creative fan - not by any stretch of the imagination. Nor am I trying to say that the only reason someone might be an acquisitive fan is because they’re complacent about issues of bias and representation, or that the only reason someone might be a creative fan is because they want to address an issue in the canon. Some people like to collect, some like to make, and some like both, or neither. It’s fine! But I do think that, when it comes to conversations about Fake Geek Girls and what being a “real fan” means - conversations which tend to be strongly gendered - the split between acquisition/creation tends to follow gender lines, too: that guys who know All The Facts and buy All The Merch are the REAL fans, whereas girls who just dress up and tell silly headcanon stories aren’t, and that maybe, there’s an interesting reason for why this might be.