How do you find more people who share your interests/passions?

I gather HN is one way, and if you are anything like me, you would have many varied interests which may or may not be shared by your friends group. Before pandemic, you could go out, meet new people, and fulfill the need. Online, its more difficult. There are forums but discovery is an issue. Like I just discovered Superman the Animated series, and unless one of my friends watches it too, I cant find anyone to discuss that with. (I am a DC fan). How do you find such forums? (Superman is just an example, talking in general about varied interests)

Apologies if it breaks the rules.