VR/MR devices that are capable of video Passthrough may display a texture of the real-world environment in the background of an application. 

Applications using Passthrough do not have access to the real-world texture for security and privacy reasons. The texture remains within the Snapdragon Spaces Services application. 

The texture coming from the engine is alpha blended together with the passthrough texture by the compositor in the Snapdragon Spaces Services. 

While applying Unity or Unreal screen space post processing has an effect on the texture rendered within the engine, the effects are not going to influence the passthrough texture captured from the real-world environment.