MacRumors published a story that Apple has released the first beta of macOS Catalina 10.15.4 to registered developers
Apple Seeds First Beta of Upcoming macOS Catalina 10.15.4 Update to Developers
Apple today seeded the first beta of an upcoming 10.15.4 update to developers for testing purposes, one week after releasing the macOS Catalina 10.15.3. update.
Apple Seeds First Beta of Upcoming macOS Catalina 10.15.4 Update to Developers