https://wccftech.com/macos-big-sur-beta-4-released-to-developers-download/

Today, Apple has seen fit to release beta 4 of macOS Big Sur to developers for testing purposes. The beta arrives two weeks after beta 3 was released to developers and over a month after it was unveiled to the public at Apple's 2020 WWDC event. If you're a developer, you can download the latest build right now from the Apple Developer Center.

If you're interested in trying out the latest beta for yourself, it is available for free from the Apple Developer Center. However, make sure that a proper configuration profile is installed from the Apple Developer Center. Once it is downloaded, here's what you have to do: