Always publish on your own platform then syndicate it across all the relevant social media providers to get exposure. It's a huge pain, especially now that most platforms are closed and don't provide automation (APIs, RSS), but it's really the most flexible solution. It also makes syndicating to new providers a lot less painful since you'll have some standard raw form (e.g. Markdown) which you can create a manual or…
What does "your own platform" mean? Without relying on things like Tor, I don't believe it's possible to publish anything without relying on some large corporation who can pull your content with a day's notice. If not Medium, it'll be AWS or Google Cloud or your domain registrar. Anyone who cares about an open web should be, at minimum, calling out those who take down content on short notice without reason.