Twitter has restricted Congressman Marjorie Taylor Greene’s account

Yes. Twitter can do this. They are a private company and can ban, censor, restrict, lock and also reset any account on that breaks their terms of service which every user on the platform has agreed to.

You can scream, criticise and protest about their decision all you want. Anti-trust or not they can and will do it again. They won't change. That's the way they are.