As of now, there is no official information about a product named Xiaomi SU7 Ultra or any official prototype video from Xiaomi at the Nürburgring (the famous motorsport complex in Germany). Xiaomi, primarily known for its smartphones, consumer electronics, and smart home devices, has expanded into various tech fields, but no known product named "SU7 Ultra" has been confirmed or associated with them at the Nürburgring.

If Xiaomi is indeed exploring vehicle technology or advanced prototypes under the SU7 Ultra name, it's likely they would release an official announcement or promotional content through their official channels. For the latest on Xiaomi's releases or innovations, you might want to follow their official news releases or check their social media updates.