https://wccftech.com/apple-releases-macos-catalina-10-15-4-watchos-6-2-and-tvos-13-4-to-developers/

Today, Apple has seen fit to release the third beta of macOS Catalina 10.15.4, watchOS 6.2, and tvOS 13.4 to developers for testing purposes. The new beta builds arrive a week after the second developer beta was released. If you're interested, you can download the latest version from the Apple Developer Center.

macOS Catalina 10.15.4 beta 3 can be downloaded on supported Macs using a profile that is installed using the Software Update mechanism in System Preferences. However, take note that you will require an appropriate configuration profile from the Developer Center.