How to enable dark mode on the Galaxy S9/S9+:
- Open your device Settings.
- Scroll down and tap on Display.
- Select Night mode then Tap on the toggle Turn on now.
- To configure Night mode, tap on the entry itself rather than the toggle. Right now, there are no configuration options. Eventually, you’ll be able to have this system-wide Night mode enable at night, just like the current blue light filter.
- For easier access to Night mode, you can also add a quick toggle in the notification shade.