How do adults genuinely make new (close) friends?

Most of the close friends I’ve had (or have) in my life resulted from school or school-related activities—growing up on sports teams, university, graduate school, etc.

Nowadays, as I approach my 30s with a desire to make new friends and meaningful social connections—I find it very hard to make new connections beyond coworkers, “acquaintances”, etc. I tend to have an extroverted personality in most situations but much of the time when I’m out of the house people appear unapproachable or preoccupied with their existing friends.

Similarly, using meetup apps feels too forced or inauthentic. In the event you do connect with someone, how do you continue to foster that into a genuine friendship without a recurring event like school, sports, etc.?

Perhaps I’m overthinking it, but it seems much more challenging and intimidating to make genuine friends as an adult and I’d love to hear your experiences and thoughts.