I'm on macOS Monterey beta 8, Xcode 13.0. When creating a brand new iOS project, then checking 'Mac' to add catalyst app, I'm not able to choose macOS 12.0. How do I make Mac Catalyst app for macOS 12.0 as the minimum? I'm using macOS Monterey new API's and they are not available when I select macOS 11.3.
See the Xcode 13 Release Notes:
Xcode 13 includes SDKs for iOS 15, iPadOS 15, tvOS 15, watchOS 8, and macOS Big Sur 11.3.
macOS 12 is still a beta at this time. The SDK for macOS 12 is included in a matching beta of Xcode, currently Xcode 13 beta 5, available from the More Downloads page.