Use APKPure App
Get Volume down BlackScreen old version APK for Android
Using VolumeDown button, toggle screen.
Press volume down button, you can toggle screen.
it's not turn off display. just show black screen.
after install and start service, press volume down and again.
it's all.
options:
Touch Enable - in black screen, you can touch or not.
Alpha.
Auto start on boot - power on device, auto start this service.
* Caution : It's not turn off display so check your battery.