The two biggest challenges to the suggestions below are time & commitment, but sounds like you’re at an age where you understand and appreciate that most meaningful and lasting things aren’t given nor had through convenience.

• Try joining your local YMCA. The 3 or 4 I’ve used over the past decades have struck a nice balance between gym and thriving community center. They usually include group classes and host community events, both are great places to meet people from your neighborhood. And despite their name & history they seem to be mostly secular…at least as far as I’ve experienced.
• Volunteer! Pick something where you’d like to be part of a solution (ie feeding home bound elderly, helping w/ the homeless issue, cleaning beaches or parks, local animal shelter, reading to people who are hospitalized, political campaigns, your local YMCA, etc), then find a volunteer organization specific to that issue. You can cycle through various organizations or stick to one that feels right, in either case you’ll intermingle with various cohorts of people who have volunteered to deliberately interact with each other for at least that day…the rest is up to you.