Substack seems to have fostered a pretty good commenting environment for the little I've seen. Especially from authors like George Saunders writing non-political / education-focused "newsletters" (i.e., blogs). In part, this seems to be because of forced login, and the fact that you have a single, shared identity for all publications on the platform (thereby increasing the value of … civility?). But also, of course, the commenters are often limited to paying subscribers, so they are all on the "same team" as it were in a way public, completely open blogs / articles aren't.