How to provide force feedback in a pedal?
Hydraulic
In a hydraulic braking system, the master cylinders typically have a spring within them that provides resistance. Also, as the pedal is pushed down, pressure buildup within the brake fluid can make it so more force is required to push further.
Pneumatic
Pneumatic systems work similar to hydraulic systems, with the brake fluid being replaced with compressed air. The master cylinders can have springs in them, or just use the compression of air in the cylinder to create back pressure and return the pedal to its original locaiton.
Varibale pressure regulators can also be used with pneumatic systems to create dynamic resistance, while one way orifices can provide resistance while pressing the pedal and easy movement on the way back.
Both hydraulic systems and pneumatic systems can also be combined with a simple external spring attached to the pedal to help return the pedal faster and provide more resistance. A torsion spring could also be investigated, but it probably makes the pedal more complex than it needs to be.
Load Cell
Another possibility is to incorporate a load cell into the pedal that conerts the pressure on the pedal to a voltage that powers a servo that can provide resistance. However I couldn’t find this being used on actual cars, rather just on pedal sets for sim racing, so it is probably difficult to implement into a car and not the best choice.