For me, it was a Twitch chat community. It started with everyone showing up the same time every week to watch a couple of people who streamed together. They eventually started a Discord server when Discord became available (which decreased the closeness of the actual Twitch chat community in some ways by making it all more asynchronous, imo, but did also solidify the community beyond Twitch in other ways). I've been to several meetups where I met many of those people, and have also separately met the two streamers a couple of times as well. I consider a number of them "online friends" to a varying degree.

I think something like Reddit would be unlikely to lead to this sort of thing, unless you're regularly participating in a small enough subreddit in a consistent/repetitive manner so as to recognize and be recognized by others (for example, I once helped run a little fanfic book club in a show's subreddit, and if that had gone on for longer, then I could see myself having gotten to know the other co-organizers a little better).

The key is probably to have some shared interest to bring you to the same place, but also an environment that's flexible enough to sometimes talk about things outside of the main interest. Older forums that would have an off-topic board were probably better about this than Reddit, since Reddit tends to segregate discussion about different topics into different places (with different people).

Mostly on technologies that enables people talking. My first online friends, were from using IRC; I even made local friends, I would never without using the online way. Then I made friends using simple emails to far away people. Next I remember I did a lot of friends using SecondLife, were i found out about "mein sonnenshein", a virtual friend i virtually married 4 times and divorce four times also (it was very cheap like 10 cents to marry and 25 to divorce, lol) and a lot of other good friends; last one i got it in a MMORPG where i saw a "beautiful" elf warrior and started talking to her, and it results she spoke the same language and were in another continent. There is been a lot of time over, but i still make contact with some of them. I would dare to say that the virtual friends were as good as the real ones, because in the end we are all humans and connected with language, and resonate in many ways.

Now a days I'd say discord is the best.

I've been running my server for about 6 years already, and it's a pretty strong community of around 20 or so people. Sometimes we get new people, not everyone is a perfect fit and they might stay for a few weeks before leaving. Some have left after a few years, some leave and come back; others come every so many months to chat for a day or two before going away.

There's many different types of relationships that can be formed in places like that.

I think what's most important is that there needs to be something you all share for it to work. Maybe it's anime, sports, whatever (in my particular case, it's an LGBT server).

I've already met around 5-6 people from this server IRL, and so far it's always been a great time.

Reddit hasn't really facilitated friendships (let alone the kind leading to real-life meetups) since the 2018 redesign at least; even before that the site was remarkably impersonal compared to any old-school forum.

Back in the good 'old' days, by playing repeatedly on the same server. On many games I've played (JK, UT, COD1-4), the servers just turned into giant chat rooms after 9pm or so. You play some games, chat a bit, then hang out on TeamSpeak.

I have no idea how people do it nowadays, gaming seems to have lost that social touch (at least to me).

You have to join a more restrict community such as the FIFA PRO Clubs or the Rainbow Six teams or whatever is restrict and gaming thing . The general chatter/board where a plethora of people hangout such as reddit won't get you anywhere just like real life

Discord's not a bad way if there's a shared interest. I met some great people on a server dedicated to a hockey team. We'd all watch the game and blather away in chat. You get to know them after a while.

Shared interests on small chat platforms. Discords for a niche subject replaced the old IRC channels. Twitch chats for small-medium streamers also work similarly (which was based on IRC!)

Instagram, actually. People try to do introduction posts in their niches (and everybody has niches) and I’ve made durable online friendships with them.

Mostly online games, forums (regular ones, not shitholes like reddit), discord servers dedicated to some specific hobbies. I met my wife on a local imageboard from my country.

I've had flesh and blood humans in front of me and it didn't feel good, maybe you're projecting.

I am the complete opposite. I like my pseudo-anonymity (I figured with enough effort some one could figure out who I am) and the freedom to be an idiot or have a bad day online that comes with that.