Pulsating brake pedal

Moin together, I register again after a while Currently my phaeton is in hibernation and far away from me, therefore nothing can test at the moment. In order to avoid damage to the stand, my father drives it from time to time. It was found that the brake starts to wobble/pulse at higher speeds (from 100kmh). Feels a little as if the ABS intervenes. Steering wheel and body feel stable, and actually it doesn’t pulsate all the time! even before, but it was never so present and didn’t happen often, even if I used to drive over the 200kmh. If it was a mechanical defect like egging brake discs, you could replicate it over and over again, but that doesn’t happen every time, only more often now. What could that be? Does the ABS come into force so quickly due to the weight or similar and the current weather? I don’t see anything in the tacho either. Or can it be from brake caliper to to be a single screw in the chassis everything?