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 First Beta of Upcoming macOS Catalina 10.15.1 Update
The new macOS Catalina beta can be downloaded using the Software Update mechanism in System Preferences after installing the proper software from the Developer Center.
It's not yet known what improvements the first update to macOS Catalina will bring, but it likely includes performance improvements and fixes for bugs that weren't able to be addressed in the first version of Catalina.
macOS Catalina is a major update that eliminates iTunes in favor of new Music, Podcasts, and TV apps, nixes support for 32-bit apps, adds a new Find My app, brings a new Photos interface, and includes multiple privacy enhancements and other app refinements.
For full details on what's new in macOS Catalina, make sure to check out our macOS Catalina roundup.
Update: According to Apple's release notes, macOS Catalina 10.15.1 introduces support for the AMD Navi RDNA eGPU architecture and brings some changes to Photos. You can now filter by Favorites, Edited, Photos, Videos, or Keywords in the All Photos view, and you can choose View > Metadata > Titles to enable titles and filenames in the All Photos View.