The display timeout of my phone Pixel 4 does not run, can I turn the display off with an app ?
Strange. This does not work ? pixel 4 display timeout - Google Search
Depending on what you actually mean; No you can not use an App Inventor app using Blocks to shut down all running apps.
I don't want shut down all running apps, only turn display off to save battery, the same thing that display timeout does after 30 sec.
A solution might be to convert your app to a foreground service Ullis Roboter Seite/AI2 Keep Alive
It may not be possible to close the screen for a single app using Blocks or intents unless the app is run as a foreground service or in the background.
Dear @patel (Andrea),
by using Brightness Tools extension (courtesy of watermelonice 
) you can set the brightness of the screen from 0 to 100%. On my phone (Xiaomi) even at 0 the display is not completely shut down, but better than nothing 'till you find something else.
Ciao !