For people who want alternatives, Ghost is a Substack-style platform that doesn't host Nazis. Its software is free open source so you can self-host if you prefer, or use Ghost's own paid hosting service.
Ghost also has Fediverse compatibility so people can follow your Ghost blog or newsletter directly from Mastodon etc. More info at https://fedi.tips/ghost-blogs-and-newsletters-on-the-fediverse/
It's free open source software (i.e. anyone can install, edit and release their own version) and the software itself is free of charge.
But you still have to pay the costs of hosting, either on Ghost.org or on your own server if you're self-hosting.
Ah sorry, I should have phrased it a bit better in my post too. I've edited it to make it clearer.