Conditionally use Big Sur SwiftUI features on MacCatalyst app without dyld crash?

I'm trying to use ColorPicker in a Big Sur Catalyst app. I thought I had wrapped everything in the correct conditionals, but I'm getting a dyld crash on Catalina:

Code Block Termination Reason:  DYLD, [0x4] Symbol missingApplication Specific Information:dyld: launch, loading dependent librariesDyld Error Message: Symbol not found: _$s7SwiftUI11ColorPickerVMn Referenced from: /private/var/folders/*/Metronomics 2.app/Contents/MacOS/APP_NAME (which was built for Mac OS X 14.0) Expected in: /System/iOSSupport/System/Library/Frameworks/SwiftUI.framework/Versions/A/SwiftUI in /private/var/folders/*/APP_NAME2.app/Contents/MacOS/APP_NAME

Here's my conditional import:

Code Block if #available(iOS 14.0, macCatalyst 14.0, *) {  ColorPicker("Display color", selection: colorBinding, supportsOpacity: false)}

I tried both macCatalyst 11.0 and 14.0 for the conditional (not being sure whether the version number is referring to the macOS number or the underlying iOS number), but neither seemed to have an effect.

My deployment target is macOS 10.15.5

Goal: I would like to be able to use ColorPicker on iOS 14 and Big Sur, but the app should run on iOS 13 and Catalina.