My first 40 subscribers came from direct friends and my LinkedIn network.
I got about 150 subscribers from a single popular post on Hacker News, posted here: >>43461618
The remainder have come from regular posting on BlueSky, Mastodon, LinkedIn, Substack notes, and starting to get search traffic from Google.
I've gotten no traction from Reddit (wow, the programming subreddits are so much angrier than every other subreddit where I contribute!) Twitter (seems like it's pay to play, which I won't do) or IndieHackers (I post milestones just for fun, but it hasn't amounted to anything).
I've found that I need to post twice a week to grow. I had a period where I was sick and was putting less effort into posts, and another period where I was dealing with a mortgage and had to post only once a week, and my subscriber growth treaded water instead of gradually growing. Even casual visitors to the site can tell the difference between moderate and minor effort.
r/programming is the only subreddit I regularly visit where there are a bunch of posts with 0 upvotes in the top 30. There are 16 right now on the Hot view.
Seems like 90% of the content there is now either reposts from Reddits first decade (2008-2018), engagement rage-bait, or really low-effort posts from newly registered users (who might be real, but they are normies so they ask really mundane boring questions that could be googled in seconds).
I truly believe it now exists only to serve as training data for the highest bidder to pay out the initial investors, everything else be damned.
I wouldn't use it for anything important.
It is frustrating though, because it makes it slightly harder to find communities of people who just want to have fun but it's better for people trying to grow a service.