disregarding the evident heteronormativity and misogyny that's baked into a lot of the way people approach same sex ships (especially m/m ships) in fandoms today, i think there's also a really interesting aspect to current fandom where even shipping a m/f ship gets colored through the lens of trying to stray from heteronormativity. you see a great deal of posts trying to subvert societal norms by making the woman the dominant one, and making her super assertive and dubbing the man in the relationship a malewife, but i find these to be rather distasteful as well, because it's become another form of misogyny on its own. the thing about trying to stray from making women unilaterally submissive is that people end up on the extreme opposite of the spectrum, which doesn't do anything about the core issue of ignoring the actual character in favor of cartoonish extremes of what their personality actually is, which, to me, is a brand of misogyny in being unable to recognize what a girl character is actually like underneath all of this girlboss talk.
the thing about fandom is that this isn't strictly limited to female characters; with male characters, you get a very similar feeling that they've been sanded down into constituent parts that are then amplified to fit them into certain tropes that they quite literally do not fit into otherwise, but the thing about female characters is that they also get hit with the extra treatment of "not being interesting enough" as a justification. i'm sure there is some movie or show or book or whatever out there where this is a legitimate thing to claim, but 95% of the time, it's a take that stems from an unwillingness to interact with the female character as someone who isn't just there to move the male character forward. there's an active effort made to find something of substance in a male character even if they're giving you literally nothing (looking at you, kpop demon hunters) while female characters get reduced to a third wheel in mlm ships. so while yes, mischaracterization is basically a fundamental pillar in fandom, i still do think female characters have it worse in that regard.
additionally, there's something to be said about how the idealized happy ending is one of a nuclear family. even with mlm ships, things boil down to finding romance, getting married, and then settling with children. i don't universally hate this, actually. i'm sure there are characters out there who legitimately might want this and it might count as a happy ending to them, but in my mind, there's a far greater amount of characters who would sooner die than fit into a "normal" nuclear family, and so this is a kind of horror in itself in my mind. i think that despite the inherent sort of "wokeness" (which i don't actually think is woke; gay relationships are natural etc etc) in same sex works that the really heteronormative conclusion of settling with a family and children undermines that. it's not like every piece of fiction ever is going to be some masterclass protest against social norms, but i would like for people to question why it is that this specific scenario is regarded as the true version of "happiness" as opposed to some other nonconventional ending. my personal qualm here is also that some of these characters would simply not make for good parents. and there's nothing you can do about that, really.
the thing about fandom is that this isn't strictly limited to female characters; with male characters, you get a very similar feeling that they've been sanded down into constituent parts that are then amplified to fit them into certain tropes that they quite literally do not fit into otherwise, but the thing about female characters is that they also get hit with the extra treatment of "not being interesting enough" as a justification. i'm sure there is some movie or show or book or whatever out there where this is a legitimate thing to claim, but 95% of the time, it's a take that stems from an unwillingness to interact with the female character as someone who isn't just there to move the male character forward. there's an active effort made to find something of substance in a male character even if they're giving you literally nothing (looking at you, kpop demon hunters) while female characters get reduced to a third wheel in mlm ships. so while yes, mischaracterization is basically a fundamental pillar in fandom, i still do think female characters have it worse in that regard.
additionally, there's something to be said about how the idealized happy ending is one of a nuclear family. even with mlm ships, things boil down to finding romance, getting married, and then settling with children. i don't universally hate this, actually. i'm sure there are characters out there who legitimately might want this and it might count as a happy ending to them, but in my mind, there's a far greater amount of characters who would sooner die than fit into a "normal" nuclear family, and so this is a kind of horror in itself in my mind. i think that despite the inherent sort of "wokeness" (which i don't actually think is woke; gay relationships are natural etc etc) in same sex works that the really heteronormative conclusion of settling with a family and children undermines that. it's not like every piece of fiction ever is going to be some masterclass protest against social norms, but i would like for people to question why it is that this specific scenario is regarded as the true version of "happiness" as opposed to some other nonconventional ending. my personal qualm here is also that some of these characters would simply not make for good parents. and there's nothing you can do about that, really.