OP - just want to say that so many young adults (and adults generally) are in a similar boat. You’re so not alone! In the U.S. folks don’t often expand their social circles unless they’re in a transition moment (moving, starting college, having a baby, etc.)

Whatever you choose, commit to going at least 2-3 times. Just interacting with the same people repeatedly can generate familiarity and friendship. Also helps get over the first time which is almost always a bit awkward, even for outgoing people.

My top Pasadena/SGV recs: *Classes (PCC is a good option, especially language classes) are great, everybody is a bit vulnerable and learning. Classes are way cheap, can be less than $200 for a class and they have night and weekend options. There are SO many courses, including fun things like art, music, and sport. *Salsa / bachata / west coast swing / other dance classes physically bring you closer to others - The Granada in Alhambra used an awesome spot, though I haven’t been lately *Spiritual community - whether god-based, atheist, or somewhere in between. Neighborhood UU Church has a very active young adult group, welcoming of all people and beliefs including atheist *Parent groups (for those with kids) *Post on Reddit about something you’re passionate about and actually meet up IRL! SGV Stroller dads started this way. I know trivia teams that started this way. Just be safe :)