Spatial Audio, a new feature in iOS 14 and exclusive to AirPods Pro, adds head tracking and surround-sound effects to compatible films. You must be running iOS 14 or higher, and your AirPods Pro firmware must be version 3A283 or higher (Settings > Bluetooth > [Your AirPods info icon] > Version) to activate this.
Tap Spatial Audio in Settings > Bluetooth > [Your AirPods info icon]. To hear the difference, switch between Stereo Audio and Spatial Audio. To hear Spatial Audio in action, play a compatible video.
Spatial Audio is supported by Apple TV+, Disney+, iTunes, and HBO Max, so watch a movie or TV show from one of those providers. If you chose a video that is compatible, you should now hear the audio shift in surround sound when you move your head, body, or iPhone.