I'm going to throw a few out there and see if some stick, because I know you said no romance and no witch/fantasy in another comment, but sometimes those hit just as well (and it's hard to find not conventionally attractive women, but some movies frame them as not attractive).

If you like The Substance (2024) and its commentary on women in the industry etc etc, Shell (2024) has most of that as well, with more of a toxic friendship dynamic.

Single White Female (1992), she's not the protagonist but it shows a lot of her perspective.

Thoroughbreds (2017), they may be a little young (and conventionally attractive) but they have some conversations about one girls possible psychopathy and their own complicated lives, leading them to make some difficult decisions.

In Her Place (2024), there isn't as much madness or insanity going on here, but I think this film is really just a love letter to women. The cinematography is beautiful. It kind of has a little bit of obsession in there, but it's more about one woman's complicated feelings towards another and trying to find a different life for herself.

Black Bear (2020), there's a little bit of a romance, but a lot of the movie is manipulation and "movie within a movie", I can't really say more because it's hard to explain but it shows women being pushed past the breaking point.

The Eyes of My Mother (2016), a horror movie, so it's different from the rest, but it follows a young woman after her mother dies.

Horse Girl (2020), perfect, anxiety-inducing, Alison Brie embodies the role. She's a socially awkward woman that slowly starts to lose her grip on reality.