As for the idea that a lot of women who ID as bi are just straight women LARPing, I think there is some truth to that

Haha it's funny you bring that one up, because that's the only one I can think of that I believe is unequivocally false. The vast majority of bisexuals aren't out and they are a lot more common than people believe. The "straight person pretending to be bi" narrative is just a way out so that any time bisexuals are criticized, someone can jump in and say "they weren't reaaally bi." It's the No True Scotsman Fallacy. I have never met a "fake bi" and doubt they exist as even a marginally significant proportion of people who say they're bi. Generally, people are thinking of bisexuals who don't appear GNC and prefer the opposite sex. Bisexuals will commonly use homosexuals for sex and then when they want to settle down, they want that heterosexual marriage. That's the biggest stereotype I was wondering about.