Mac users who want to be a part of Apple’s beta testing program can sign up to participate on the beta website, which gives users access to iOS, macOS, watchOS, and tvOS betas. Potential beta testers should make a full backup before installing macOS Big Sur, and it may not be wise to install the update on a primary machine because betas can be unstable…
https://www.macrumors.com/2020/08/20/apple-seeds-macos-big-sur-public-beta-2/