With the release of iOS 15, Apple allows you to turn off Night Mode permanently if you wish. Night Mode automatically turns on when the smartphone’s camera detects a low-light environment.
However, if you wish to do it, you can disable it if your iPhone is running iOS 15.x. Here’s how:
Go to Settings app > Camera > Preserver Settings.
You can use the toggle to enable or disable Night Mode. Voila! You’ve disabled Night Mode off on your iPhone.