Universal Control had been enabled in macOS Monterey beta 4 before the remark was abruptly removed from the release notes. MacOS Monterey beta 5 is currently available for developers, but Universal Control is not available in this version.
For developers who have already enrolled, macOS Monterey beta 5 is currently available through OTA. If you haven’t yet installed the beta, you can get it via Apple’s Developer page.
A completely revamped Safari, a Shortcuts app for the Mac, FaceTime’s new SharePlay function, Universal Control to operate seamlessly across different Apple devices, a new Focus mode, Quick Notes, AirPlay to Mac, and more are among the new features and enhancements in macOS 12 Monterey.
As always, installing early betas on your primary machine is a terrible idea, as problems and performance difficulties are widespread, so utilize a separate Mac if at all possible.