Open Settings
Tap Accessibility
Tap Display & Text Size
Turn on Reduce White Point
Adjust the Reduce White Point slider to a higher percentage
Open Settings
Tap Accessibility
Tap Zoom
Turn on Zoom
Triple-tap the screen with three fingers
Tap Choose Filter
Select Low Light
Open Settings
Tap Display & Brightness
Turn on Dark Mode
Lower the brightness slider in Control Center
Turn on Night Shift
Turn on True Tone if available
Use a black wallpaper
Enable Auto-Brightness in Accessibility settings
Use Low Power Mode
If needed, use Guided Access to keep brightness settings fixed