The biggest one is r/chapotraphouse and its spinoffs, along with r/dankleft, r/breadtube, r/genzanarchist, and probably leftbook and several youtube channels.
Red fascists infiltrate the mod teams of these spaces and initiate left unity policies that successfully ban all criticism of their backwards conservative views. The more vocal opponents of the new policy are quickly purged for breaking left-unity, leaving a more passive audience who are ripe for indoctrination.
Then the propaganda starts. Endless authoritarian memes to normalize gulags, guillotines, firing squads, violent struggle sessions and genocide. Tomes of nonsensical ideological "theory" that serves to brainwash young people who are starved for identity and belonging. Almost immediately, any ideas that conflict with the writings of Marx, Engels, Lenin, Stalin, Mao and Xi create desperate cognitive dissonance in their minds and the kids angrily lash out at the unindoctrinated for being "libs" and "imperialists" rather than risk parting with their new-found identity.
Once the majority in the space are comfortable joking about murdering "kulaks", and quoting Chinese state media to counter "western propaganda", the shaming campaign begins.
Anyone in the space who breaks with the tankie party line is lambasted and ridiculed into submission. The remaining anarchists in the space now find themselves hopelessly outnumbered by smug middle class white genocide fetishists telling them they're imperialist CIA stooges for thinking the Uighurs maybe shouldn't be put in concentration camps.
In order to not be shunned by their peers, the anarchists adopt an obscene anarcho-tankie ideology that allows them to favor libertarian writers like Chomsky and Kropotkin, while embracing the authoritarian third positionist dogma enforced from the top down by their chosen community.
Uncritical support for every nation (and empire) that opposes the "West", the insistance that anarchism and communism are one and the same because "they have the same end goal", the claim that anarchist communes and an ML state can co-exist in harmony, the attempt to whitewash authoritarian concepts like the dictatorship of the proletariat and the vanguard, the nonsensical belief that they can be an anarchist and also a Marxist. Suddenly they're able to take completely contradicting ideas and fuse them together in order to be accepted by the red fash echo chamber they so desperately want the approval of.
The conflicting ideas grow increasingly out of whack the further down the rabbit hole the left unity space takes them, and the ridicule they get for their remaining libertarian attachments begins to eat at their ego, until finally they post "How I went from an anarkiddie to a principled Marxist-Leninist" and the transition is complete.
Tldr: Left-unity is a deliberate ploy by disturbing groomers to indoctrinate impressionable young minds into their authoritarian third positionist fascist ideology and force them to abandon any libertarian beliefs they once had in order to be accepted within the collective's rigid hierarchy and not be branded a liberal or an anarkiddie for forming their own thoughts or questioning their leaders narratives in any way.
"Left unity" is nothing more than tankie doublespeak for "obey us or be purged".