Friendships form when you repeatedly interact with the same person. This is not likely to happen at a random bar, but it most definitely can happen in a cooking class, when volunteering, playing music with people in a band, routinely getting together every Thursday night with others in your local makerspace and so on. Especially if you have to actually work together: perhaps offer your help to a local cause you support, perhaps a CoderDojo?

Also, FWIW, very few adults still know their childhood and high school friends and most people gradually lose the friends they make in college. It's just what happens, and while it will be harder for you to form new friendships, we all have to work at it. I don't know anybody who'd say "alright, I now have all the friends I desire, I hereby declare a ban on new friendships."