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
Safari Crashing for Both iOS and Mac Users, Fixes Identified [Update: Fixed]
URL searches, autocomplete, Top Sites and other Safari features rely on queries being sent to and returned by Apple's servers, suggesting this is where the problem lies. The issue also seems to depend on what data the browser most recently cached.
The current fix for iOS and Mac involves disabling Safari Suggestions, which stops the app from crashing to the home screen. On your iOS device, go into Settings, tap Safari, and toggle off the "Safari Suggestions" switch. On your Mac, the same setting is found in Safari -> Preferences -> Search.
Alternatively, opening a Private Browsing window also appears to solve the issue.
The problem appears to be affecting users around the world and will likely be resolved when Apple corrects the service on their end.
Update: According to BuzzFeed, Apple has now fixed the issue that was causing the Safari browser to crash on iOS and Macs due to issues with Safari Suggestions.