I was in the driver's seat in one-pedal driving. The car was stopped. I attempted to move the vehicle up a few feet so the driver in the car behind could reach the microphone to order their meal. When I tapped the gas pedal, the car moved slightly, but the engine revved loudly and thoroughly; the iX50 then launched itself forward, and I applied the brake. The brake pedal went to the floor. The iX50 launched violently forward. It struck the stopped full-size SUV in the rear. That vehicle came to a stop, literally 20-25 feet forward. The iX50 then hit the steel pole there to protect the drive-thru window. The steel pole came entirely out of the ground. The BMW app on my phone generated a message that the iX50 had a brake failure, that the suspension was unstable, that the iX50 should not be driven, and that the wheels should be blocked so that it could not roll.