Honestly, this is the wrong question, but I understand the intent. What you really should be asking is "Where is the online community for your hobby/interest?"

The thing with HN, is it works for the startup/hacker/tech community, and that community has evolved here over time. If you want a link/topic sharing site for other interests, the answer is almost always going to be a subreddit.

But if what you really want is to be immersed in a community, those communities will be in weird corners that you have to discover. The reason for this is that a community almost always wants to be semi-private: discoverable by others that share the same interest, but just far enough out of the public eye to not get bombarded with bots/trolls/obnoxious people

Some examples I know of:

  - Voron (3d printer)? You want to be on their discord
  - BigGreenEgg (kamado smoker)?
  - MMA? sherdog
  - Electronics/Robotics diy style hacky projects? hackaday and go to the comment secion
The cool part about finding these true pockets of a community, is you can learn a ton about what truly makes them tick. What do they get excited about, what do they have an irrational hatred for, etc. If you've ever asked yourself "how do I market my app/website/saas", it's almost certainly because you haven't yet encountered where that niche community resides, and are falling back to more generic strategies. Find the community, and they'll tell you what they want in spades
Not exactly what you're asking for, but a few people appreciated when I shared this last time a similar post came around:

Nice conglomeration of headlines/links from lots of different sources. Lots of tech and science, but also a good mix of global news. Includes HN actually.

I've stopped following pretty much everything except HN. Which is unfortunate (though sorta nice for my mental health), but my interests right now are also narrow.

I'd suggest Lemmy? It still feels small, and has decent activity for self-hosting and homelab stuff after the whole reddit API debacle. That's where I plan to put more effort once I stand up my own ActivityPub server. Id like to try Mastodon again too but I bounced off last time

Fishbowl if you are into consulting.

Kind of an old gen site and isnt without its issues, but I feel like metafilter gives me a few good links every day still so I keep it around. They are good at spotlighting stuff that is lesser known.

lowtechmagazine if you are interested in very practical sustainability. Their solar powered website (a 1-board computer on somebody's roof in barcelona) has been a recurring HN topic.

ibz is the equivalent of HN for bitcoiners and the only one I read daily besides this one...
Twitter is actually pretty cool if you find the right people to follow in the topics you’re interested in.

You can also make lists of such people so they’re separate from your main feed.

It does feel harder to comment on stuff though. Not sure why?

There are some excellent topic-specific subreddits IMO. Like:

  - /r/ProgrammingLanguages
  - /r/Compilers
  - /r/EmuDev
  - /r/DatabaseDevelopment (disclosure, I run this one)
Are there really any? HN has the quality it does thanks to dang's tireless efforts, and I don't know of any other site with similar moderation.
Not identical as a "users create all content" but (and .io) is excellent for tech stuff. Think DIY meets crazy scientist.
Other sites to follow: science tech math finance LINUX physics pick category to skim at top pick category to skim at top
For bioinformatics:

For them intersection of tech builders and bio people: Bits in Bio Slack

I really like Tildes

which is less focused, more about everything (god I wish I could frontpage an article about sports on HN) but has a much higher ratio of discussions to links (e.g. Ask HN is a joke)

I have invites.

Aviation Herald is, somewhat curiously, something like a HN for airplane related incidents:

Related, sorting by tags and date
alexchantastic is somewhat similar in terms of active discussion for investing and personal finance. Unfortunately, it’s in a forum format so threaded discussion is a bit difficult.
Not sure if you can really find something like HN for other topics. HN works as it works exactly because of the topic and audience. Same structure might not work for other things
I am making, which is supposed to be old-digg-like link aggregator site. I would have it out by now if only I could stop procrastinating T_T

Like HN, with tags. Not many people yet though.

Reddit still has some good communities
This is any subreddit.
I’ve been enjoying

A sort of incipient decentralized blockchain hackernews

I can build one if you want lol.