You can find friends doing volunteer work, taking courses that interest you, various meetings and groups. You may need to either find a group that draws you in, or try to genuinely talk to people and get to know them. If your goal isn't to be friendly, nothing much will happen.

Fwiw I do/have done those things. I have many acquaintances that will greet me in the street or whatever.

There focus here isn't me, and I'm trying to keep it that way: I mean to say that these things may help but shouldn't be viewed as sufficient.

There's something else needed, for sure. IMO only people who you spend time with outside of the original context are really friends - like someone you have as a colleague might become more than an acquaintance when you, say, go to a (non-work directed) event outside work together. There needs to be some sense of choosing to be with one another, not just happening to be in the same location because you both like volleyball, say.