sigh... ya helga was a total asshole towards her.. but on the other hand... she's kinda a bit of drama queen on the smallest things

yeah but it doesn't look like a reason to hate her (I mean the fandom)

well i did grow up watching the cartoon and how helga treats her.. O_o sibling rivalries can sometimes be a lil messed up... specially for olga and helga's case

it wasn't a "sibling rivalry" actually, cuz it takes two
and Olga always was just a nice girl, she didn't even take part in this conflict
the problem is their parents, obviously

oh ya... those two also has issues... O_o like serious issues like her dad is super overconfident as hell and always has his head in his own company while her mom.. okay i gotta be honest her mom has really serious sleep issues and always down all the time... O_o just gonna say that paltaki family is nuts as a whole

well it's implied that their mom is an alcoholic, so it's a bit deeper than just sleep issues
and looks like their father is an abusive narcissist or something

O_o yeowch... well i was a kid at the time so i don't i was able to pick that up easily i just basically laugh at the parents stupidity and naturally facepalm at helga's mood swing moments... but once on a blue moon i just facepalm at the parents sheer stupidity also

And both have a tendency to pick favorites. There are times the two sibs do reach common ground tough. Olga even told Helga that she feels like, "a broken wind-up doll" so much is expected of her from her parents like she's the begin all, end all. Except the end, she's as much a victim/target as Helga is (not disregarding Helga's past sins towards her mind you).

Yes, she's a victim of their parents but also a victim of her sister's aggression
I fully understand why Helga behave like this and I have no questions towards her, I just found out that many people hate Olga for nothing

There can be numerous reasons for this.
1. They only see it from Helga's perspective only. What they remember is "Olga the snooty little miss perfect who has all the glory and everything goes her way and their parents absolutely love and adore her while Helga is shoved aside and considered the failure child."

2. Some people may feel like they were the overshadowed sibling, so they feel more like Helga in reality, and so they despise Olga too.

3. The parents are the main cause for the animosity between the sister. Their clear favoritism and absolute disregard for Helga is without a doubt the cause of Helga's bitterness and spiteful behavior. Being the neglected one, Helga is ignored and can't really do anything to call out this behavior. Olga, however, is in a position where she can call it out, but never does cause she seems to be ignoring the situation just as much as their parent ignore Helga. So people may despise her for never attempting to fix either Helga or her's relationship with their parents.

4. From the viewer's perspective, it may look as though Helga has done more to help Olga than Olga has. While they may see Olga sacrificed herself to go teach in Alaska, Helga stepped up to save her from marrying a conman. While Helga has done things to sabotage her sister, she has always fessed up and attempted to communicate her issues with Olga, who seems to "hear"... but not really "listen".

5. Helga is a reoccurring character frequently seen, while Olga is an "outsider" rarely seen.

Any combination of these could be what gives people cause to dislike Olga. Honestly, I don't like Olga, but looking back on having typed all this, even I myself feel pretty bad for both sister, and want to smack their parents. lol

Yep, I thought about all of it too :D
I guess for the younger viewers it's difficult to see the situation from Olga's perspective, and also such situation is pretty common and may trigger some people
Olga tried really hard to become closer with Helga, and she really loves her but she can't just fix their parents, so that's all she could do
And the reason why their relations don't change through the series is the series format - all episodes are completed and separated stories, so everything just stays as it is
Moreover, Olga is rarely seen, as you've mentioned, and such a problem can't be solved just for one day
Olga is not my favourite character, but she's obviously nice and is not to be blamed, as well as Helga

and yeah, their parents suck, and Miriam makes me feel a bit anxious, like she's not only ignoring her kid, but also feels like she's dangerous and unable to provide safety, let alone emotional comfort and care
Bob is just stupid, but at least he can't cause physical harm