This app helps to activate the Android dark mode on devices that do not provide this option in the system settings.
This app will not work on all devices since some smartphone manufacturers disabled this option for their devices!
Devices running on MIUI 10, especially the Redmi Note 4 are having some issues when updating from MIUI 10 to MIUI 11.
The dark mode functionality of your phone might be disabled after updating to MIUI 11.
Your phone could be stuck in either Day Mode or Night Mode, depending on what was active before the system update.
I'd recommend deactivating the dark mode before updating your phone to MIUI 11