Still learning. At Substack I have to manually enable free commenting on a per-post basis. All the archived posts from here that were imported are default pay-to-comment except for "You're not a dog, Ya'll!" which I just now manually changed to test it. I'll check for an alternative setting, but that's what I'm stuck with for now.
The result is I'll need to get to editing some of the recent posts. A pain. Going forward I can do that as part of writing and publishing a post.