Antifa https://en.wikipedia.org/wiki/Antifa_(United_States) came from Antifaschistische Aktion(German antifa of 1930)
https://en.wikipedia.org/wiki/Antifaschistische_Aktion which was created by the Communist party of Germany
https://en.wikipedia.org/wiki/Communist_Party_of_Germany with one of its two founders being jewish .
https://en.wikipedia.org/wiki/Rosa_Luxemburg
But according to conservatives "Antifa are the real fascists". This is why conservatives lose when they can't even correctly identify what their enemies are. Antifa are neither fascists nor nazis, they are communists that the fascists and nazis had fought with.
If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.. --Sun Tzu art of war
"Fascism" in common parlance isn't the same as actual, historical fascism, and I don't think people are really suggesting they're the same. Instead, it gets pointed out that antifa behave along similar lines to fascists through violent, coercive control, and censorship and oppression of dissenting speech. In doing so, they act on behalf of the established leftist government to circumvent opponents' constitutional rights, which is another hallmark of fascism. They intimidate to crush dissent and they're clearly authoritarian.
Fascism is a left wing authoritarian ideology. The so called "antifa" is in favor of left wing authoritarian government, and mergers of state and corporate power (when it benefits them), as seen by their simping for corporate political action. That is fascist - merger of state and corporate power. They do advocate for fascism, just not the exact fascist party platform of WW2 eras.
It is ridiculous that they call the party that in theory wants reduced and decentralized government power fascist, while advocating for a functionally fascist system.