I also don’t understand how I’m supposed to be attracted to a gender, it being a personal and subjective feeling.
Agreed; being attracted to a particular type of gender identity sounds a bit of an impossibility (though I'm going to try to make sense of it in the next paragraph). But it's perfectly possible to be attracted to either gender-conforming or gender-non-conforming people - some lesbians only go for butches, some for femmes, some for an androgynous look, and some aren't fussed either way; and there are plenty of straight women who only fancy men who do the stereotypical-masculine thing of short hair and trousers, and aren't remotely attracted to men in floral dresses and eyeliner.
The sense I can find in there is: we have this model of attraction that puts the physical body first and foremost, and assumes that attraction to the body comes first. For some people, this may be true; for others it's not the case, and the determining factor is effectively personality.
But then they go and muddle it all up with absolute batshittery like: bisexual is offensive because it connotes there are only two sexes and the underlying valid point - that we are forcing everyone into a model of sexuality based on the experience of the typical heterosexual male - is lost amongst the bickering.
FWIW my best mate is bisexual and gets proper pissy whenever anyone tries to tell her she's pan, or queer, or anything else. She's happy with bi and feels it describes her proclivities perfectly well, and doesn't want to be forcibly reidentified. And she doesn't fancy woks either.