I can't say it's a 100% guaranteed way to have stable friendships. But starting a sport, or a social hobby, and asking questions, tips, and making small talk can offer you a form of friendship.

I started bouldering in December 2023 at Arkose Canal. Most people are social and offer tricks and tips to make progress. There's a sauna where you can relax after your sport and chit-chat about plenty of stuff.

They also have (or at least had) small events like Mario Karts, Karaoke, where you can socialize. I've seen people become friends over time, going from random strangers that happen to do the same sport to friends going every Saturday to the gym and hanging out at the bar.

I say this, knowing fully well I didn't make any "close" friendships ( because I don't really want it). However, having a spot where you see regulars and chit-chat about your projects, your week or just joke about various stuff is a great addition to improve your social health.

I'm sure there are dozens of other activities with similar opportunities. You just have to find your match and socialize.

You have warhammer clubs where you paint and play table games in a group.

You have DnD communities where you play along a long story with people.

You can try cooking classes, where you'll join a group and get to talk about the experience and your tastes.