Adult find a friend
For example, if you're a libertarian vegetarian who lives in Minnesota and you like dressing in clown make-up and juggling live sharks, there's probably a meet-up for that. Cause it's not like you don't already have 30 million bajillion things to do. If you do it regularly, you'll meet people who care about the same things you care about.
You can join Meet-ups about gardening, board games, politics, cooking... But it's not like those super boring classes where you have these huge papers and you have to do all the work in your group projects. If you don't meet people, you'll still use your talents to do something good for the world.
It isn't impossible but I can admit from experience it definitely feels like it.
It's because you aren't being yourself in interactions and you end up not saying things of value, based on what you really think or feel.So far that, not to sound too pessimistic, it's toxic in many ways.But anyway we shouldn't dwell on that broadscale problem because it's very unlikely society can be changed in our lifetimes.They don't want that power and you need to learn it's what's best for you too.
So yeah none of this is straightforward but that's because friendships are not straightforward. I know there can be great friendships in store for you.
But the actually doing it...well, it's about as fun as a brief encounter with a freezing cold speculum while your panties are in a wad on a plastic chair in a freezing cold (and poorly lit) office. OK, so maybe I'm being dramatic, but unless you're one of those natural social butterflies or one of the rare birds who still regularly hangs out with all your high school friends, finding new people is tough. Even science has looked at the issue of adult friendships and found that without serious work, it's basically all downhill once you hit your late 20s.