The Yamaha Disklavier has solenoids on every key, so you could disable every key but the one you want by moving them downwards. It already has a similar featur

The Yamaha Disklavier has solenoids on every key, so you could disable every key but the one you want by moving them downwards. It already has a similar feature called SmartKey: https://www.youtube.com/shorts/_Qj33POZCyA https://www.youtube.com/shorts/_Qj33POZCyA