What an interesting question. GQ. The way you framed it adds dimensions to the basic query. Thanks for sharing it.
Beyond casual acquaintances, two of my best friends were people I met at work. We got to know each other gradually over time—months, years—mainly through lunchtime conversations, and later through interactions outside the workplace. It always takes me a long time to get past the safe surface stuff. By now we go back thirty years or more.
Several more were people I met through social groups and support groups. In particular, doing volunteer work for a voluntary association was a way to connect, as well as supplying some common ground. Working alongside someone takes a lot of social pressure off, and again, you can take your time about it.
In the case of support groups, by their nature they have you revealing a lot of inner stuff, usually not pretty, and you have to extend your trust before you can say anything. It’s a different dynamic and can be a bit scary, but it does clear away a lot of obstacles.