When in public view, you cannot hide your game from spectators.
Features that help me focus & reduce eyestrain or spectator distractions: Zen mode [Z] key; Chat disabled ☑; Full screen [F11]; 2D Chessboard size ⇲ [Blue]; Piece set [governor].
For a private game: Use the board editor analysis and select the icon «Practice with computer».
https://lichess.org/analysis/rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR_w_KQkq_-_0_1
As soon as a player starts playing chess, someone else could be spectating the game though a window; simply by hovering their mouse over the user names. The spectator user names are not displayed, until they show up in the game link, like OTB showing up in the room.
If distance is what you need to concentrate, use Zen mode. Think of it like you are playing OTB in a private room, where cameras are the only thing that are visibly monitoring the game.
