That's like saying there is no such thing as communism. There is such a thing as communism, it is an ideology, not an organization. The Communist Party USA is an organization, not an ideology.
Antifa, in the US context, is used to describe an organization that doesn't exist. People were protesting various causes, but very vocal right-wing extremists started using that label to imply there is an organization which they can blame for alleged violence.
That's like saying there is no such thing as communism. There is such a thing as communism, it is an ideology, not an organization. The Communist Party USA is an organization, not an ideology.
You can fill in the rest.