MacRumors published a story that Apple has released the fourth beta of macOS Big Sur 11.3 to registered developers.

Apple Seeds Fourth Beta of macOS Big Sur 11.3 to Developers

Apple today seeded the fourth beta of an upcoming macOS Big Sur 11.3 update to developers for testing purposes, with the new beta coming two weeks after the launch of the third beta and more than a month after the release of macOS Big Sur 11.2, a bug fix update. Developers can download the ‌‌‌macOS Big Sur‌‌‌ 11.3 beta using the Software Update mechanism in System Preferences after installing the proper profile from the Apple Developer Center.  ‌

Apple Seeds Fourth Beta of macOS Big Sur 11.3 to Developers