[CAT0]

Title is wrong.

Cyberpunk 2077 beats Elden Ring, but is far from the most played single player game on Steam.

[andrewguenther]

Title is mostly correct. Cyberpunk 2077 currently has the highest number of concurrent players on Steam of any single player game.

[dragontamer]

Single-player only game.

Which means Factorio and Civ6, among others, are right out of the discussion. Because those games support multiplayer, even if its relatively rare to have multiplayer games on those.