What we need to do is stop using one "main" platform. The problem was centralization. We need to make so many more platforms they cannot possibly shut them all down. Parler is gone? Make two more new startups!
Keep multiplying as they shut 'em down. It's how piracy has kept on going, and it'll work even better for alt tech because unlike piracy alt-tech isn't illegal. (Well not illegal yet anyways.)