Just about any hobby can be a group hobby. I run, bike, hike, rock climb, watch sports, drink, try new restaurants, play video games, travel, and shit post. All of these can be done individually or in a group. My old man likes stamps and guns. There are shows and meet-ups for that too.
What are you in to that can’t be done with others? If these are truly solitary activities then are you willing to give something new a shot? Try something new and if you don’t vibe with the peeps or the activity, try something else new the next time.