> As I write this post, my neighbors from above, probably college students, are having a party of their lifetime, laughing, kicking and screaming. I'm not even mad at them, just full of envy.

If you're fun (warning: it sounds like you're not fun), you can probably just party with them. We're the same age and I've had girlfriends that are still in college. It's not weird if you're not weird about it.

If you haven't had kids and aren't boring, 18+ is a valid dating range.

> Finding friends in my teens and 20s was as easy as going out literally anywhere.

It still is, you're just going to the wrong places or presenting yourself wrong.

> When I eventually went to work, I thought my life would only get better. And I made a good career, but in the process, steadily drifted off into isolation.

I think there may be some naivety here. Work is to acquire capital, to invest in assets, to generate capital, to avoid work. Work is not supposed to be fun or satisfying. Work is supposed to acquire capital.

I think in previous generations, you could ask coworkers out on dates, but that's dangerous and most SWEs are remote now anyway. It's best to keep work to just work.

> they're all full of lonely developers and other socially awkward people - short guys looking for girlfriends, unattractive/aging women looking for husbands, etc.

If that's not your scene, then don't go to those places. Find something that's cool and happening now and meet people doing things that excite you.

If the goal is young women, you can be in your 40s and find plenty of college girls interested in age gap relationships.

> All the "normal" people I knew in the past are now changing diapers and working to pay off their mortgages, which I guess is a kind of consolation.

The people I know with kids end up so defeated that they essentially martyr themselves with employment to give their children a better future. I understand that people willingly make this choice, but it's not for me. It's really good to see times changing and the idea of "normal" going away.

> Still, I'm only in my 30s, and it feels like my life is pretty much done. Doing things by myself is boring and depressing, and getting into a group of "normal" friends, of both genders, to hang out and laugh with, seems like an impossible goal.

This is your error because it's not impossible. I've seen whole communities of old people form meaningful friendships and they're all 70+.

It might be impossible for you while you're doing your career. That's ok. People will still be around when you're done working.

If you're at the peak of your dev career in your 30s, you can probably be retired by 40 with some good negotiation/investment.

> In case someone has any advice beyond finding a hobby, going to therapy, approaching random strangers, it would be greatly appreciated. I don't have any skills other than coding, so quitting the career would be a major financial hit. On the other hand, I feel that finding a non-coding job would be ultimately the best way to find new social groups, and get out of the apathy

IMO you're already in deep enough that you might as well see it through. Try to get a job with high total comp, work hard for a few more years, retire before 40. Learn enough about investing and finance that you don't screw it up.

Then simply do things you find legitimately interesting that involve other people. It's important that you actually care about the activity, so you can be happy and confident and present at your best.

You can't just "try ballroom dancing" and expect to meet a new group of cool friends. Compete with cool people at doing cool things, and then you'll have groups of cool friends.

Maybe audition for a rock band. Or start an NFT project. Or become a nature youtuber. Or dance on TikTok. Or whatever you'd do anyway, once you're not tied down by a tech job.