The real magic/genius are trailer brakes, they are electric right, however if they worked the way you would naively assume an electric brake would work, directly operating on the friction surface with an electric solenoid, It would take a huge solenoid and the amperage requirements would quickly exceed what the trailer wiring can provide. so what they do is apply an electromagnet which starts to drag on the side of rotating wheel assembly it uses this drag to push the friction surfaces together, so it takes a surprisingly small magnet to run. most of the force comes from the rotating wheel.
That's the "self-applying" property of drum brakes. Not specific to trailer brakes.
They're actually really simple? Two wedge-shaped brake shoes that cam into the inner diameter of the wheel.
More not easy to servicd if they seized and you can disassemble half the car to get to all the cables and so on
You can almost always pop the cable (if you have to) and hit the rotor with a hammer, or use a puller.
If that doesn't work you hit it with a hammer from the other side until the parking brake shoes pop out of the pins and come off with the rotor.