Does night shift work on installed apps?

Night Shift operates at System Level. Screen brightness and colour temperature will be adjusted system-wide.

Dark Mode, by contrast, requires explicit App support.

I hope this clarification is helpful.

The Night Shift feature and Dark Mode feature are two distinctly different iPad features.

The Night Shift feature is a global, system-wide iOS feature that is designed to minimise the iPad's blue light emanations at night.

It is known that blue light emanating from tablet screens is what keeps one awake at night.

By changing the color spectrum of tablet screens from predominantly blue ( cooler) hue to more of a yellow or warming color hue, this reduces our visual exposure to the blue hue light that emanates from our tablet and phone screens and with more intensity in darker environments.

The Dark Mode ( black background screen/white text feature ) is NOT an iOS global feature and is specifically a per app, coded-in feature to turn the screen all black with white text ( to attempt to completely eliminate all blue gamut light ).

All apps will have the Night Shift mode feature, while not all apps will be coded to use the Dark Mode feature.