Ben Thompson is working on Passport, which seems to be a self-hosted (WordPress-based) Substack: https://stratechery.com/2021/passport/
replyHe gave a talk on it at WordCamp Asia at the start of last year, although I haven’t heard of any progress recently on it.
You're missing the point of Substack:
reply1. It's a social media platform with a network that is still easy to extract organic growth from.
2. 99% email deliverability without configuring anything. It's whitelisted everywhere.