3.1 Identifying Your macOS Version
When developing with SwiftUI, the Xcode 12.2 environment requires a system running macOS Big Sur (version 11.0) or later. If you are unsure of the version of macOS on your Mac, you can find this information by clicking on the Apple menu in the top left-hand corner of the screen and selecting the About This Mac option from the menu. In the resulting dialog check the Version line.
If the “About This Mac” dialog does not indicate that macOS 11.0 or later is running, click on the Software Update… button to download and install the appropriate operating system upgrades.
Figure 3-1