Apple today seeded the second beta of an upcoming macOS Monterey 12.3 update to its public beta testing group, with the new software coming a week after the first macOS Monterey 12.3 public beta.
Public beta testers can download the macOS 12.3 Monterey update from the Software Update section of the System Preferences app after installing the proper profile from Apple's beta software website.
Universal Control is the major new feature in macOS Monterey 12.3, and it is designed to allow multiple Macs and iPads to be controlled using a single mouse/trackpad and keyboard. If you have a MacBook Pro and an iPad Pro, for example, both devices can be controlled with the MacBook Pro's trackpad and keyboard or a keyboard attached to the iPad.
iPadOS 15.4 is required for Universal Control on the iPad, and once the updates are installed on your devices, the feature just works as it is automatically enabled.
macOS Monterey also includes new Emoji 14 characters like melting face, biting lip, heart hands, and more, and plus it adds support for updating AirPods with a Mac. There's no official update interface, but your AirPods can receive firmware updates over-the-air when connected to a Mac, similar to how the update process works with an iPhone.
There are some under-the-hood changes as well. Apple is removing Python 2 from macOS with macOS 12.3 after support was suspended in January 2020, and Apple is eliminating some kernel extensions used by Dropbox and OneDrive, necessitating software updates for those apps.
Source: Macrumors