What Catalina feature lets an iPad act as a Mac's second display? Sidecar.
Apple introduced Sidecar with macOS Catalina in 2019, allowing a compatible iPad to work as a wireless external display for a Mac. Users can extend the desktop, mirror the Mac screen, and move windows between the two devices. The connection can also use a cable, which may improve reliability.
Sidecar is more than a basic monitor feature. With Apple Pencil support, the iPad can function as a pressure-sensitive graphics tablet for Mac applications such as image editors. Compatibility depends on the Mac, iPad, operating-system versions, and Apple-account requirements.
A common mix-up is AirPlay, which can mirror or stream content between Apple devices but is not Catalina's dedicated iPad-as-second-display feature. Continuity Camera instead turns an iPhone into a Mac webcam, while Stage Manager organizes open windows.