SAE J2807 tow ratings allow for trailer brakes to be required, for tow ratings over 3,000 pounds. The owner's manual will state the threshold when brakes are required in order to be compliant with this standard. Some vehicles can achieve max tow rating without trailer brakes (Ford Explorer is one example), but modern pickups with their huge numbers absolutely require them.
2020 F150 Owner's Manual wrote:
"Important: The towing vehicle’s braking system is rated for operation at Gross Vehicle Weight Rating, not at Gross Combined Weight Rating. Separate functional brakes should be used for safe control of towed vehicles and for trailers where the Gross Combined Weight of the towing vehicle plus the trailer exceed the Gross Vehicle Weight Rating of the towing vehicle."
FWIW - the actual standard for trailer stopping performance is:
The combination is required to stop completely from 20 mph in 80 feet or less. During this stop test, the trailer must remain within an 11.5-foot-wide lane throughout the entire stop. In addition to the active testing, the parking brake must be able to hold the truck and trailer firmly in place both upward and downward on a 12 percent grade when it is at the maximum GCWR.
