App Standby allows the system to determine that an app should be idle when you are not actively
using it. The system makes this decision when you does not touch the app for a certain period of
time. If the device is unplugged, the system disables network access and suspends syncs and jobs
for the apps which seem idle.
You can choose not to optimize a particular app either from Doze or App Standby from app
info or battery settings.
First, The condition for App Standby:
What happens to the app when the app is in standby.
To exit from standby mode, you need to simply charge the device or launch the app
directly or indirectly.