No camera feed on SCNTechnique

Hi,
I have a SCNTechnique pass `scene_only`, and I was expecting the camera feed to be rendered to a texture `scene_out`, snippet below, but when I debug the GPU, it's just black for the pass, do I have to specify another parameter to capture the camera feed too?
Seemingly related: https://stackoverflow.com/questions/59569525/scntechnique-on-arscnview-does-not-affect-camerafeed-scene-background-on-ios-1

  <key>scene_only</key>
  <dict>
  <key>colorStates</key>
  <dict>
  <key>clear</key>
  <true/>
  </dict>
  <key>excludeCategoryMask</key>
  <string>1</string>
  <key>draw</key>
  <string>DRAW_SCENE</string>
  <key>inputs</key>
  <dict/>
  <key>outputs</key>
  <dict>
  <key>color</key>
  <string>scene_out</string>
  </dict>
  </dict>