This again…

Antifa existed back then and were about as opposed to the allies as one could be

They were the militant branch of the German Communist party, who fought tooth and limb against the Social Democratic Party (the National Socialist's main opposition). At times, they even worked together to crush the SDP, even going so far as to call the National Socialists "The working people's comrades" and accusing people with western political views of fascism.

They were dispatched of after the Nazis rose to power, of course, having served their time as useful idiots, but this would not be the end of them.

After WW2, they supported the Berlin Wall, calling it the "Antifascist Barricade"… from the soviet side (peak irony). That is not one, but two global conflicts in a row where they sided with actual authoritarians many would today call fascists.

If you had a time machine, and went back to call an Allied Soldier "Antifa", they'd give you a VERY confused look.

And had you spoken to an Antifa member of the time about how great it was the Allies were coming… you'd have earned a quick beating and been called a fascist.

Not only is this "The Allies were the original Antifa" dumb, it's also objectively wrong and backwards.