Apple today seeded the second beta of macOS Big Sur to developers for testing purposes, two weeks after releasing the first beta following the Worldwide Developers Conference.
The macOS Big Sur beta can be downloaded through the Apple Developer Center and once the appropriate profile is installed, subsequent betas will be available through the Software Update mechanism in System Preferences.
As with all of the new betas, Apple recommends not installing macOS Big Sur on a primary machine because it is early release software and could have major bugs.
Read more at MacRumors.com