MacOS Monterey
macOS Monterey (version 12) is the 18th and current major release of macOS, Apple's desktop operating system for Macintosh computers. The successor to macOS Big Sur, it was announced at WWDC 2021 on June 7, 2021, and released on October 25, 2021.

The operating system is named after Monterey Bay, continuing the trend of releases named after California locations since 2013's 10.9 Mavericks.

Changes 
Monterey introduced several new features and changes, including:

Shortcuts for the Mac
TestFlight for the Mac
Provisions to allow the planned introduction of Universal Control, which allows a single keyboard and mouse to control multiple Macs and iPads. It works on Mac computers with the Apple M1 chip and some with an Intel processor, including MacBook Pro (2016 and later), MacBook (2016 and later), MacBook Air (2018 and later), iMac (2017 and later), iMac (5K Retina 27-inch, Late 2015), iMac Pro, Mac mini (2018 and later), and Mac Pro (2019). It works on these iPads: iPad Pro, iPad Air (3rd generation and later), iPad (6th generation and later), and iPad mini (5th generation and later).
Support for Apple Music Voice Plan Subscription.
Portrait Mode and Noise Cancellation features for FaceTime and some apps (in Control Centre)
New Toolbar Features/Designs for Finder and Preview App
Have a Live Memoji and Animoji right on the lock screen
A yellow privacy-indicator on the menu-bar for indicating if Mic/Webcam is Active 
Live Text, which allows a user to copy, paste, translate and lookup text from images displayed by Photos, Screenshot, Quick Look, and Safari. 
New Passwords Manager for Mac
A New On-Device ML-Activated Keyboard Dictation using Siri and also now for almost unlimited duration.
Low Power Mode for Mac which enables longer battery life for lightweight workflows like Reading PDFs, Web-browsing, Listening to Music, etc. This works on MacBook (Early 2016 and later) and MacBook Pro (Early 2016 and later).
 A redesigned optional compact interface for the Safari browser.
 Support for playing AirPlay content streamed from recent iOS and iPadOS devices and Macs, including: MacBook Pro (2018 and later), MacBook Air (2018 and later), iMac (2019 and later), iMac Pro (2017), Mac mini (2020 and later), Mac Pro (2019), iPhone 6s and later, iPad Pro (2nd generation and later), iPad Air (3rd generation and later), iPad (6th generation and later), and iPad mini (5th generation and later). Older iPhone, iPad, and Mac models may share content at a lower resolution to supported Mac models when "Allow AirPlay for" is set to "Everyone" or "Anyone on the same network" in Sharing preferences.
 Improvements to FaceTime, including the ability to share a screen and the SharePlay function that enables multiple users to watch or listen simultaneously and in sync (e.g., to music or TV shows).
 The ability to factory reset the device from the System Preferences app
 Visual Look Up makes it easy to identify objects (eg- Cat Breeds, Dog Breeds, etc..) found within user's photos.
 Focus to set different modes to filter notifications across iPhones, iPads and Macs.
 The Time Machine backup functionality excludes more system files.
 Provisions to allow the planned introduction of "Expanded Protections for Children" which will apply cryptography to detect and help limit the spread of child sexual abuse material (CSAM) online by scanning the user's iCloud photos.
 Accessibility option to change the mouse pointer's colors.
 Tips notifications.
The removal of a previously bundled PHP interpreter.
 The removal of the ability to use custom Quartz Composer filters and plugins in Photo Booth.
 networkQuality, a command-line tool for measuring upload/download capacity, upload/download flows, and upload/download responsiveness
 An automatically populated "Games" folder within launchpad 
 Support for ProMotion in new M1 Pro/Max MacBook Pro

Applications

Notes 
In the Notes application, users can now apply arbitrary tags to a note (e.g., #cooking, #work); groups of notes with a given tag or tags can be viewed in Smart Folders or a Tag Browser in the sidebar. The new Quick Notes function enables a user to create a note from within any app via system-wide keyboard shortcut or hot corner.

Maps
Apple Maps adds a 3D globe, with increased mountain, desert, and forest detail.

News
Apple News has been completely redesigned, featuring more rounded corners.

Shortcuts for Mac
Shortcuts are activated manually through the app, shortcut widgets, the share sheet, and Siri. They can also be automated to trigger after an event, such as the time of day, leaving a set location, or opening an app.

Game Center 
Game Center adds the ability to view and accept friend requests, invite players to games, and share game highlights when using certain game controllers.

System requirements 
macOS Monterey drops support for various Macs released from 2013 to 2015 including all Macs with Nvidia GPUs. Monterey works on all Macs equipped with Apple silicon SoCs, as well as the following models equipped with Intel CPUs:

 MacBook: Early 2016 and newer
 MacBook Air: Early 2015 and newer
 MacBook Pro: Early 2015 and newer
 Mac Mini: Late 2014 and newer
 iMac: Late 2015 and newer
 iMac Pro: Late 2017
 Mac Pro: Late 2013 and newer

macOS Monterey can be installed on earlier computers that are officially unsupported by using patch tools, such as the mid-2014 iMac and the 2013 MacBook Pro. Using these methods, it is possible to install macOS Monterey on computers as old as a 2008 MacBook Pro and iMac and 2009 Mac Mini.

Release history 

12.0 was pre-installed on 2021 MacBook Pros and Apple advised those with the version to be updated to 12.0.1.

Known problems
Users and developers have reported:
 Problems with trackpads, such as tap-to-click not working and gestures being misinterpreted (fixed with 12.1 update)
 Inability to use Bluetooth devices reliably (unresolved), inability to use Bluetooth PAN (feature removed)
 Laptops unable to boot (fixed with 12.0.1 update)
 Inability to charge sleeping laptops with MagSafe. (fixed with 12.1)
 App memory leak issue
 Inconsistent performance with external USB hubs transferring data (unresolved, 12.1)
 Battery draining issues (fixed with 12.1)

References

External links
  – official site

2021 software
ARM operating systems
Computer-related introductions in 2021
17
X86-64 operating systems