Communities exist among all kinds of topics. Regional and local specialties are found in food, entertainment, jobs, schools, and more. Communities exists on many platforms. Few successfully span, for instance, Facebook and discourse or reddit.
“Read the room” is a popular phrase meant as a cue to listen to the substance of the conversation before sharing insight, aka offering an opinion. It’s especially good advice in online communities, where sarcasm and some other forms of humor do not always send the same message as intended.
Communities grow around concepts, locations, and products that have broad approval and use. Fishing is a concept. Canva is a product. Lake Wobegon is a location. Examples exist is large numbers.
Communities need not require thousands of members to be effective or entertaining or insightful. Read through an hour or day or month of posts, depending on the pace. It gives an idea of the value you can share and learn.