MacRumors reports that Apple has released macOS Catalina 10.15.4 Beta 3 to registered developers.
Apple Seeds Third Beta of Upcoming macOS Catalina 10.15.4 Update to Developers
Apple today seeded the third beta of an upcoming macOS 10.15.4 update to developers for testing purposes, one week after seeding the second beta and a month after releasing macOS Catalina 10.15.3.
Apple Seeds Third Beta of Upcoming macOS Catalina 10.15.4 Update to Developers
The new macOS Catalina beta can be downloaded using the Software Update mechanism in System Preferences after installing the proper software from the Developer Center.