Jรผrgen Habermas’s The Structural Transformation Of The Public Sphere (1962) defines the “Public Sphere” initially as “conceived above all as the sphere of private people come together as a public”. This can be simplified as a metaphorical “bubble” which people enter into to when wanting to debate topics.
Another source describes it as the “social space in which different opinions are expressed, problems of general concern are discussed, and collective solutions are developed communicatively” (Wessier, Fruedenthaler 2018). It is the place people go to discuss the news, issues and topics that grab their attention or cause concerns.

Each individual has their own separate bubble of people they go to to discuss topics with, which for myself is with my various groups of friends (weird flex, but ok) as well as the Reddit communities of Subreddits.
For example, I have different groups of people I go to for different topics, such as surfing, tennis, basketball or regular news. These spheres often communicate via various group chats over Snapchat, Instagram, Messenger and in-person.
Some members are active in multiple groups, and often multiple conversations occur at the same time. Major topics of conversations include memes, films, tv shows, controversial news and ethical scenarios.
The media plays a large role in this process, as social media allows for interaction to occur within these spheres, by providing the topics of conversation, as well as the means to communicate anywhere you are, and to comment your thoughts on various posts.
With the amount of topics to discuss, I believe it is nearly impossible to belong to only one Public Sphere, as where one group may not find a certain topic interesting or worthy of discussion, another group may, which is where each person will go to find another group willing to discuss that particular topic.
For example, in the show Spongebob Squarepants, the character Squidward Tentacles (pictured above) prefers to talk to the title character, Spongebob, about working at the Krusty Krab and keeps his private life as private as possible. Whereas, in the episode House Fancy, talks to Nicholas Withers, a fellow house decorating enthusiast about his house, despite the disastrous occurences that take place during the episode.