Apple has seeded developer betas of macOS 10.15.2, iOS 13.3, iPadOS 13.3, tvOS 13.3, and watchOS 6.1.1.
Registered developers can download the betas via Apple’s developer portal (https://developer.apple.com/account/#/welcome). Or they can be downloaded over-the-air once the proper configuration profile has been installed from the Developer Center.