https://wccftech.com/apple-seeds-first-beta-of-ios-13-4-5-macos-10-15-5-tvos-13-4-5-to-developers/

Today, Apple has seen fit to release the first beta of iOS 13.4.5, macOS 10.15.5, tvOS 13.4.5 to developers for testing purposes. The latest beta builds arrive a week after the company publicly released iOS 13.4, macOS 10.15.4, and tvOS 13.4. if you're a developer, you can download the latest beta builds from the Apple Developer Center right now.

Starting off with iOS 13.4.5, you can download to from the Apple Developer Center or via the over-the-air mechanism. However, a proper configuration profile is required from the Developer Center. At this stage, there is no word why Apple decided to use iOS 13.4.5 instead of iOS 13.4.1. At this point, we're not sure what the new beta build adds apart from bug fixes and performance enhancements.