Apple has released the updates to macOS Monterey 12.1, and Big Sur 11.6.2, with the next Catalina Security Update 2021-008. For M1 Macs, the 12.1 update is a substantial 3.2 GB download, and around 2.83 GB for Intel models.
Monterey 12.1 and Big Sur 11.6.2 are only available as updates through Software Update and
softwareupdate, or as full installer apps through the App Store and
softwareupdate. A standalone installer package for Catalina Security Update 2021-008 is now available from here, but Apple doesn’t provide such standalone updates for macOS 11 or 12.
These updates bring firmware updates to all models.
Monterey 12.1 introduces SharePlay at last, Apple Music Voice Plan, the enhancements to Memories promised for Photos, Digital Legacy for iCloud, and more.
Among the bugs fixed are blank Desktop and Screen Saver options, unresponsive trackpads, charging from external displays, kernel panics in HDR video playback on YouTube.com, a notch issue on 2021 MacBook Pro models, and MagSafe charging stopping on 16-inch MacBook Pro 2021 computers. There’s no mention of fixing any memory leaks, but initial testing here suggests that at least two of the known leaks have been fixed, in coloured pointer and the Control Center, but not in Finder File/Find, which does still leak steadily.
Fuller details of the changes in Monterey 12.1 are given in this article.