I am not able to find any permision for app in Android that keep Screen of the mobile always on. I tried through adding permision in android manifiest but did not work.
For your reference:
Make sure you are updating the right file. Again, if you build your app again, the file will be overwritten and changes will be gone. So, you may create a build-template to preserve your changes.
could you please tell me the name of the activity(for android) that I need to put the FLAG_KEEP_SCREEN_ON in?
also, for native platforms, can I create a .java and a .mm file in the required directories in the build-template folder?
You can put FLAG_KEEP_SCREEN_ON at AppActivity.java.
build-template will copy (or overwrite) all files to your original build path after build task is finished, so you can put any files you want to change.