Instead of a gym another options are joining volunteer groups, a fraternity order (Oddfellow / Rebekahs), a local D&D meetup or local motorcycle club. Sharing a common interest is the easiest way to make new friends.

> “do your hobby with other people, frequently”

>

> On paper, the gym seemed like the perfect opportunity to meet people since I would go there nearly every day

Yeah, the gym is the authors interest.