The new MacOS Mojave 10.14.6 beta can be downloaded via the software update mechanism in System Preferences after the correct profile is installed from Apple's Development Center.
We do not yet know what improvements the next update to macOS Mojave will bring, but it is likely to include bug fixes and performance improvements for issues that could not be addressed in macOS Mojave 1
MacOS 10.14.6 is probably one of the latest updates to the MacOS Mojave operating system MacOS Mojave that Apple will soon be transitioning to work on MacOS 10.15, the one not named the next generation version of the macOS operating system.
Apple will debut macOS 10.15 at the Worldwide Developers Conference, set to kick off on June 3. While it will be in beta testing for several months before you see a fall release, the work of today's software often slows down when Apple is ready to launch new software.