Set Chromecast screen status to idle

I'm trying to find a way of telling my Chromecast with Google TV screen to idle - do you know how to do this from Node-red? I want to do that since I've set it to display selected photos when in Ambient mode. I've seen nodes that will report the status of the screen, specifically whether isIdleScreen is true or false, but not found anything that will actively instruct the Chromecast to idle. Currently I use the physical remote and press the Back button to get the Chromecast to idle as I want, but I'd like to be able to control it from Node-red (or openHAB or Harmony). Thanks

I've the Google TV app on my Android phone which has a remote control capability. Below is a screenshot of the remote control on which I've highlighted the button that tells the Chromecast to idle the screen. Is there any way I can identify what instruction is sent by my phone when that button is pressed? If I could identify the instruction, then I could reproduce that in a Node-red flow, but I've no idea how I might analyse what the phone app sends.