We’re past the point of registrations across multiple states
LOL, no we’re not. Biden hasn’t even been nominated yet. The earliest deadline is Ohio, which is requiring the Democratic party to do a special virtual vote to get on, but that’s still in the future.
Your link is a list of filing deadlines for the primary.
So maybe after being wrong and accusing everyone else of being foreign agents, check your own information sources that are trying to convince you of this.