Bruh, a toxic relationship also includes manipulating your partner. Just because no psychical harm was included, doesn't means the relationship isn't toxic. As you said, you've never been in an toxic relationship, so you literally have no say in it.
Hwayeon doesn't act that way? Sure, according to your image of toxic relationships. "doesn't hurt anyone except the store manager", are we even reading the same shit here?? She literally just scratched or punched jisoo on the face. And as for the extreme part, girl its just a fictional character
MC and Hwayeon are most likely just friends with benefits as you can tell from the early chapters. She feels guilty for getting close to Jisoo because she feels some sort of obligation to Hwayeon for helping her in a tough time. Clinging to Jisoo? She's just literally interested in Jisoo, how do you even see it as clingy bruh.
yk just bc Hwayeon "only" spread rumors and lies doesn't make her any less toxic. dont take spreading rumors too lighty as well , it can affect a person's reputation and life.
Her jealousy towards Jisoo is pretty toxic as well , she won't even let the MC hang out w her and even assaulted Jisoo are you just gonna excuse that and let it slide ? And how is it clingy if a person just wants to get closer to someone ? was the MC that annoying to her ?
1. If you've never EVER come close to being in a toxic relationship, you do NOT have a single right to decide WHAT is NOT toxic. If you do NOT understand WHAT is a TOXIC relationship, you do NOT get to define it. Whatever the fuck you're describing as a so-called toxic relationship is no longer toxic, it IS straight up abusive relationship.
2. Being manipulative is actually a behavior of an abusive person. So, either way, it's worse.

I've never been in a toxic relationship, so idk, but my imagine about toxic relationship would be that your partner abuse you, talk shit, casually yell at you, force you to do something you dislike, do bad things to you/family/friend. That's how a toxic relationship should be.
Hwayeon doesn't act that way. I know Hwayeon's manipulative, she spread rumors about Jisoo (to her friends), told lies (doesn't hurt anyone except the store manager). However, it doesn't go extreme for you guys to hate and talk shit about her so much.
How about MC? What is the relationship between her and Hwayeon? Friend with benefit? If so, why does she felt guilt for getting close to Jisoo? Lover? If so, why is she clinging on Jisoo too much?