Toxic Yuri Manga
Manga
This is a collection of (mostly newer) yuri series that fit the moniker "Toxic Yuri". These stories feature problematic girls and lots of drama. Common themes are cheating, manipulation, obsession, noncon, and abuse.
Zenbu Kowashite Jigoku de Aishite
If That's Love, Break It.

Manga, ? vol, 2023
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Author:7
Abuse is heavily explored in this one, but perhaps in a slightly more nuanced way then you're expecting. Every character in this story is struggling with their own demons and taking it out on others.
Kyou wa Kanojo ga Inai kara
My Girlfriend's Not Here Today

Manga, ? vol, 2021
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Author:7
Features one of the most unlikeable main characters of all time, but that's exactly what makes it so engaging. Yuni has no idea what she wants and so she strings along both her girlfriend and the girl she's cheating on her with, leading to truckloads of yuri angst.
Utsushicha Dame na Kao
A Face You Shouldn't Show

Manga, ? vol, 2023
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Hostess x celebrity yuri with toxic BDSM elements
Usotsuki Hanayome to Dousei Kekkon-ron
The Lying Bride and the Same-Sex Marriage Debate

Manga, ? vol, 2023
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Certainly not the most toxic on this list (as of the translated chapters currently out), but it does include a "straight" woman cheating on her husband and some potential manipulation going on. Considering it's the same mangaka as Netsuzou Trap, I think it belongs on this list, based on what I've read so far and the potential for some dramatic escalation.
Kitanai Kimi ga Ichiban Kawaii
I Love Your Cruddy...

Manga, 5 vol, 2019
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This one features some somewhat extreme/gross fetishes (not saying that to kink shame, just as a warning, lol). Imagine a monster-of-the-week series, but it's sadistic fetish-of-the-week

Manga, 9 vol, 2020
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Fairly unique premise for a yuri story. A girl can see people's corpses one day before they die. Plenty of blood, death, and girls fighting.

Manga, ? vol, 2024
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The dynamic in this one is really enjoyable. Kamaki and Wakaba have always been rivals and are constantly making bets with each other, but Wakaba always loses. The price she pays is giving away her dignity to Kamaki and following any orders she gives her. Kamaki starts stealing all of Wakaba's "firsts" as their relationship and rivalry evolves. The sadism in this one isn't as extreme as some other series on this list, but it's present, lol.

Manga, ? vol, 2024
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Another "girl does increasingly sadistic things to her classmate" story. There are not a lot of chapters out yet, but it's promising.

Manga, ? vol, 2024
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Really pretty art style, really dark story. If you're looking for a yuri that features two girls murdering and dismembering the body of an abuser while looking like sparkly princesses, um, here you go I guess!

Manga, 4 vol, 2019
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Teacher x Student yuri, and oh boy is everything about this toxic and extremely problematic
Watashi wo Tabetai, Hitodenashi
This Monster Wants to Eat Me

Manga, ? vol, 2020
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Anime adaptation coming soon! Monster girl yuri
Futsuu to Bakemono
The Story about a Monster Teaching Common Sense.

Manga, ? vol, 2022
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If I had a nickel for every yuri about a monster girl wanting to eat the other one... well, I'd have two nickels, but it's weird that it happened twice. The monster girl in this one is a lot more malicious
Keiyaku Shimai
Contract Sisters

Manga, ? vol, 2022
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Features a woman and a high school girl who enter into a contract to pretend to be sisters. It's fairly light-hearted, but the ten-year age gap and sister thing is pretty problematic.
Mahou Shoujo ni Akogarete
Gushing over Magical Girls

Manga, ? vol, 2019
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Author:7
Primarily on this list because it's so controversial. It's an over-the-top BDSM comedy that is more ecchi than romance.

Doujinshi, 1 vol, 2023
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Only four chapters, so makes for an extremely quick read.
Saji-chan no Yami Nikki
Sajichan's Sick Diary

Manga, 2 vol, 2017
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Edgy yandere comedy yuri
Soshite Kaede wa Hanayaka ni Saku
And Kaede Blooms Gorgeously

Doujinshi, 2 vol, 2018
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no limbs amputee girl x slave girl. you read that right.

Manga, ? vol, 2022
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obligatory incest yuri inclusion. generally pretty silly in tone, but the obsessive nature of both of the sisters, and well, the fact that they are straight-up biological sisters is enough to label it as toxic for me.

Manga, 11 vol, 2015
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The ironically titled "Happy Sugar Life" goes beyond the simple toxic label into deeply fucked up territory. The MC is a murderer who has fallen in love with a child she kidnapped.