Requirements - Social Dummy Version 5.0.5 or later. iOS 13 or later.
Go into your device Settings app
Tap Display & Brightness
Tap Dark mode
Tip
For an easier switch of Light/Dark mode, you can add the widget into your Control Centre.
Go into your device Settings app
Tap Control Centre
Tap Customise Controls
If not done so already, tap the Dark Mode control.
Once enabled, you can quickly switch between Light/Dark mode whilst in any app.