A few more steps...

macOS 12 Monterey Developer beta profile has started downloading.

After the download process is complete, you can double-click "macOSDeveloperBetaAccessUtility.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:

Learn how to unenroll your devices to stop receiving developer betas ↗