> “do your hobby with other people, frequently”.

I think it's decent advice, but from my experience, it can take years to make friends that way. I practiced various sports my whole life in the context of sport clubs (martial arts, climbing, snowboarding, swimming...). The way it worked for me is that after months, sometimes years of chitchatting with same people over and over, I barely made any good friends from that context. I did make a bunch of "acquaintances". Definitely better than staying home, but not a silver bullet.

Often i sit around a coffee shop where i work frequently as a remote employee, and I think to myself, "there could be another person here that i have the capacity to be really good friends with but i will probably never know it." And I think about how that's probably true of other people in that coffee shop.

The engineer in me wants to believe some technological solution to finding and connecting with potentially great friends is out there, waiting to be uncovered. But of course, an engineer would say that.

Yes it's very easy to just let things sit at the "acquaintance" level. You know people at the gym, or at work, or at whatever recurring thing that brings you together. But to extend that to friendship, you need to invite them to do something outside of that. Get lunch, come over for dinner, game night, movie, whatever you're into. And then they need to reciprocate at least somewhat evenly. If this doesn't happen it's not really a friendship. And (in my experience) it's very rare for adults to progress beyond the "acquaintance" stage.

The unstated bit is that you have an incidental excuse to talk to them (compared to cold approaching in other contexts) but you still need to talk to them. Everything depends on you making the effort.