Is there any shortcut to turn on flashlight in Android?

A non-root method I propose here requires AutoInput, Tasker (both are paid apps with full free 7 day trial), TeslaLED and AutoShortcut.

Instructions:

1. Setup all the apps and launch Tasker

   
   



2. Profile 1: Event → Plugin → AutoInput → Key → Configuration

   
   
   
   
   • Keys: Home
   
   
   • Key Action: Key Down
   
   
   
   



3. Task for Profile 1: (Actions):

   
   
   
   
   1. Variables → Variable Set: %Set to 0
   
   
   2. Task → Wait: 1 Second
   
   
   3. Task → If: %Set eq 0
   
   
   4. Plugin → AutoShortcut → Configuration → TeslaLED Toggle
   
   
   
   



4. Profile 2: Event → Plugin → AutoInput → Key → Configuration

   
   
   
   
   • Keys: Home
   
   
   • Key Action: Key Up
   
   
   
   



5. Task for Profile 2: (Action): Variables → Variable Set: %Set to 1

   
   

The explanation for the instructions can be found at the bottom of my answer for Prevent Accidental Reboots when holding down the power button.

As for the duration of long-press, the minimum I could satisfactorily test was one second (Wait action manages it). If your device is fast enough, you may have some good results for milliseconds. Configure Wait as per your wish.

Also, alike my other answer, the long-press for screen off would work if there involves a traditional hardware button (like Power button) which can be pressed and not simply touched.