Ultrasonic static is easy to filter out if it is even picked up by the microphone. You'd need something broad band but in the hearing range, like ... music.

Or have sane privacy laws that are actually enforced? You can't solve issues like this with technology on a local scale.

Companies generally comply with legalisation. GDPR is far from perfect but EU companies adjusted since it is just the price of doing business.

or use the cone of silence