I'm rooting for her to grow but it's valid to hate her. She's selfish and rude, very quick to assume things about other people she doesn't even know. She has no agency beyond doing everything for her ex boyfriend, doesn't even work or have a job, and has no idea how to properly interact with people because her boyfriend would always be like "oh please forgive her for being rude she's just like that hahahaha." She doesn't even stop to think "maybe my ex broke up with me because I have no personality beyond him," and instead just decides to make her ex jealous to get back with her? I'm honestly surprised she has any friends, considering that she doesn't listen to them and doesn't even have any money to pay for her own food during hangouts. She oversteps boundaries as well. She has less maturity than most teenagers do despite being an adult.
Feelings are constantly changing and it's okay to hate the FL and then grow to like her as the story progresses. Right now I hate her and think she's a self-entitled and obnoxious brat that I wouldn't like to work with or even interact with, considering she's barely a person (she has no goals other than be coddled and love) but as she grows and is exposed to the world perhaps I will come to like her - I hope I do.
I mean you’re right about it being valid to hate her but I do want to say that some people are exactly like her I knew a person who was selfish and rude and couldn’t NOT have a boyfriend all the time but sooner or later they do grow up and regret the shitty things they did, which hopefully the FL becomes aware of in the future but I think she DOES have a personality like you said she’s rude but it’s not all black and white and I think this webtoon is trying to show that, that the rude self untitled girl slowly redeems herself by realizing the hard way that what she did in the past was not ok. Some people need to learn first hand to learn something than people telling them it’s wrong,, also now that I’m thinking about it no one seems to tell her what’s right or wrong too tho they gossip about her character but never tell her up front that she’s rude and what she’s doing wrong and cause her boyfriend never even told her why he’s breaking up with her and what maybe she did wrong so I don’t think it’s entirely her fault that she’s trying to get back together with her ex through a weird jealous plan kinda way, it a little of the ex’s fault too for not telling her what’s on his mind and what he thought about her. Idk this is my theory but it kinda seems like he was just using her for her looks and never talked to her about the important relationship stuff and just bought her stuff so she wouldn’t break up with him... but I also hope you come to like the FL when she grows as a person too.

Some of y’all wayyy to quick to hate on the FL, I like her she doesn’t know what’s right all the time but that’s what makes her human.. she’s not gonna be perfect and/or smart at the beginning of the story