The game is written for a group of three to five players and one game master (though there's nothing mechanically that says you can't try it with a player and a game master, or eight players and two game masters, if that's to your liking) with room for some back-and-forth regarding narrative control.
That said, the Pressure mechanic forms a potentially very useful baseline for an inventive player to hack in solo play, and I would be thrilled to hear how it goes from anyone who'd make the attempt.