https://wccftech.com/apple-seeds-beta-6-of-macos-10-15-4-tvos-13-4-watchos-6-2-golden-master-to-developers/

Today, Apple has seen fit to release beta 6 of macOS Catalina 10.15.4, tvOS 13.4, and watchOS 6.2 Golden Master build to developers for testing purposes. The updates arrive a week after the fifth beta was released to developers and a month after the previous version of the firmware.

If you're a developer, you can download the latest build from the Apple Developer Center. macOS 10.15.4 can be downloaded on your supported Macs using the Software Update mechanism in System Preferences after the appropriate configuration profile is installed from the Developer Center. macOS Catalina 10.15.4 will add Screen Time Communications Limits, Real-Time lyrics, and much more once it's here.