https://wccftech.com/apple-releases-beta-3-of-macos-big-sur-11-3-to-developers-download/

Apple has seen fit to release macOS Big Sur 11.3 beta 3 to developers for testing purposes. The third beta arrives two weeks after the second beta was released and a month after the release of Big Sur 11.2. If you're interested in testing it out, you can download it right now on your compatible Macs. Let's dive in to see some more details on the build and whether Apple has added any forward-facing features.

If you're a developer, you can download and install Apple's macOS Big Sur 11.3 beta 3 on your compatible Mac models through the Software Update mechanism in System Preferences. Make sure that a proper configuration profile is installed from the Apple Developer Center.