They are many automation programs available in Android. It would be nice if the Android Spacedesk app could issue an event when it loses connection with the desktop. A user could then trigger that event to turn off the screen using automation software.
The only recourse I have now is to use automation to turn the android screen off between the hours of 11PM and 7AM. The rest of the day if my primary display turns off or my PC goes to sleep, I get to see the scrolling disconnect message.
We have released a new spacedesk Android viewer in the Play Store. This release can now automatically let the client device enter suspend mode when the primary PC is turned off/suspended. Please try it on your side and let us know your feedback regarding this feature.