As mentioned previously, Substack is a mailing list subscription service. It supports monetization by subscription fees, does not run advertising or track users, and does not organize content by an algorithm. Other than the fact that it is centralized, it is as decentralized as possible, focused on providing a producer-subscriber relationship without interfering. One might expect, then, that its moderation policy would be "none", but it isn't quite. Their guidelines prohibit porn, hate, plagiarism, impersonation, doxxing, criminal activities, and spam and phishing. This is a pretty reasonable starting point. These guidelines wouldn't work on a broadcast service like Twitter or algorithmic service like Facebook or YouTube, but if you as a subscriber are able to choose what you see, then these should be sufficient.