Apple has released iOS 13 beta 4 to developers for testing with the build number is 17A5534f, two weeks after unveiling the new iOS 13 beta 3 updates at the Worldwide Developers Conference.
iOS 13 introduces new features like Dark Mode, new browsing and editing tools for Photos, Sign in With Apple, enhancements to Maps, updates to Reminders, Notes, Messages, Siri, CarPlay, Files, and much more. More details here
Downloading and Installing iOS 13 Developer beta 4
The registered developers can download and try the iOS 13 beta 4 from Apple Developer Center or via OTA(over-the-air) mechanism with the proper configuration profile that can be installed from the Developer Center.