MacRumors published a story that Apple has released the third beta of macOS Catalina 10.15.6 to registered developers.

Apple Seeds Third Beta of Upcoming macOS Catalina 10.15.6 Update to Developers

Apple today seeded the third beta of an upcoming macOS Catalina 10.15.6 update to developers for testing purposes, three weeks releasing the second beta and over a month after releasing macOS Catalina 10.15.5 with battery health management features for Macs.

  Apple Seeds Third Beta of Upcoming macOS Catalina 10.15.6 Update to Developers