Literally pick any half-organized activity. They’ll be posted all over the Web (sorry, you will probably need a Facebook account), your city’s website may have lists of organizations, and there are probably some fliers posted at the library (and the library may run a few gatherings themselves!)
Those are so important! I often struggle to suggest activities other than sports
Piggy backing to add - running clubs, book clubs, board game clubs, church if you're religious.