Lower tire pressure means more contact surface area with the road for gripping during braking.
As a result, maximum braking performance should be obtained at the lowest possible tire pressures (dependent on factors like vehicle weight, max speed,..)
Higher tire pressure reduces grip levels for the same braking torque on the wheel due to reduced contact area, resulting in a longer braking distance.
Braking distance is affected by a variety of other factors such as tire compounds, surface tire, and weight distribution, which are more difficult to control than tire pressure.