We have several things we do for fun. This changes with time and this is because our needs change too. Some years back, I didn't have any fun activities, staying indoor was enough for me but that changed with the introduction of smartphones. Chatting online with friends became what I do for fun and sometimes playing mobile games, this continued until 2017 when chatting became a burden.
I have just a few friends and I'm often the busy type who's up and down trying to make a living. But I often spare time to hang out and cool off my head, mostly on my own or with a friend. This is what I do, I spare the weekends to hang out on my own, to a place that's bustling and watch people dance or do what they love to. I prefer to just watch and enjoy the moment. I often don't participate. Watching people alone seems to give me some joy that I can't explain.
I checked up what the dictionary says about the word fun, and it refers to enjoyment, amusing, or something pleasurable. If I'll go with the first word "enjoyment", then I'll say eating good food is what gives me the feeling of enjoyment, but then, hanging out is what I do for fun, usually after a stressful day or week, I go out and allow myself to enjoy the moment. As an ex-introvert , I don't have a lot of things I've caught up with for fun. For now, hanging out alone or with a friend gives me that fulfillment at that particular time.