How to disable android phone's display?
Thanks @mnd I found solution for the problem.
The following app works smoothly. It disables only display 

https://forum.xda-developers.com/android/apps-games/app-screen-backlight-off-xda-exclusive-t3037380

Thanks stackexchange family.
Source: How to make an app behave the same way with screen off, as with screen on?