It depends. Mediation participants may be in the same room or different rooms. Whether you engage in on-line dispute resolution (ODR) or in-person mediation, you choose whether you see each other.
The Bruckner Mediation office offers three meeting rooms along with a conference room. When participants choose to be in separate rooms, and the mediator goes back and forth between the rooms, it is called a caucus. The participants may stay in caucus for the duration of the mediation or may convene at some point.
Most mediations currently occur on-line through a Zoom platform. The Zoom platform allows all participants to meet in a main room akin to a large conference room. It also allows participants to meet in private conference rooms, which Zoom calls breakout rooms.