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 Seeds First Beta of macOS 10.15 Catalina to Developers
The new macOS Catalina beta can be downloaded from the Apple Developer Center, and once installed, subsequent betas will be available through the Software Update mechanism in System Preferences.
As with all new betas, you're not going to want to install macOS Catalina on a primary machine as it is early release software and could have major bugs.
Apple delved into cross-platform apps in macOS Catalina, porting additional iOS apps to macOS and overhauling some existing apps. There are new Music, Books, and Podcasts app, with the iTunes app being retired.
Apple is also making it possible for developers to bring their iPad apps to the Mac with just simple changes, which will make it simple for developers to create cross-platform content while also increasing the number of available Mac apps.
You're able to use the iPad as an external display thanks to new continuity functionality built into macOS Catalina and iOS 13, and there's a new "Find My" feature for locating lost devices and friends even when your devices have no cellular or WiFi connection.
macOS Catalina is only available to registered developers at this time, but later in the summer, Apple plans to make a public macOS Catalina beta available, giving public beta testers a chance to try the software before it sees a public launch in the fall.