
A few more steps...
macOS Big Sur beta profile has started downloading.
After the download process is complete, you can double-click "macOSDeveloperBeta16AccessUtility.dmg" file.
And install the pkg installation package:

Follow the prompts on screen and enter your password to install
An update can be detected in System Options - Software Update:

Please backup your Mac before installing macOS Big Sur.
Learn how to unenroll your devices to stop receiving developer betas ↗