I don't actually know what "Antifa" is, if it is in fact anything specific (rather than, e.g., a banner used by many and disparate groups--maybe that was your concern?).
What I did mean is that declaring certain organizations to be terrorist organizations (HAMAS, Al-Qaeda, etc.) seems to be well within the remit of the executive branch.
Antifa is not an organization. It's an ideology. There are groups that call themselves anti-fascists, which have different views and methods, and there is no HQ they answer to. Just like MAGA.
Another example: banning zionism/antizionism or banning racism.
It can't work like that.
The focus has to be on criminal acts committed by individuals, regardless of their ideological affiliation.
Banning an ideology would be a direct and fundamental attack on the 1st amendment of the constitution.
It would lead to "guilt by association." A concept the Supreme Court has found to be unconstitutional. (NAACP v. Alabama (1958), Scales v. United States (1961), Noto v. United States (1961), United States v. Robel (1967), etc.)