The breaks will always be engaged in manual mode when the Flexpendant’s 3-position switch (dead man switch on the side) is not held in the center position.
In auto mode, the breaks will engage after two minutes of robot standstill. You will hear a click from the controller, and the drive fans will turn off. The motors will stay on. So as soon as the controller gets a move command, the brakes will disengage automatically.