Night mode is an automatic setting which takes advantage of the new wide-angle camera that's in the iPhone 11 and 11 Pro models. It's equipped with a larger sensor that is able to let in more light, allowing for brighter photos when the light is low.
macOS Catalina Now Available
Apple Releases iOS 6.1.1 for iPhone 4S Devices, Fixes 3G Issues
A beta of iOS 6.1.1 was released in the middle of last week carrying a build number of 10B311 -- it's likely the upgrade released today was an urgent bug fix and the prior iOS 6.1.1 beta sent to developers will become iOS 6.1.2.
About iOS 6.1.1 Software UpdateThanks to @AppleNicholas for the screenshot
This update fixes an issue that could impact cellular performance and reliability for iPhone 4S.