In Paper (the legacy renderer) we implemented the conversion for PlatformColor / DynamicColorMacOS / ColorWithSystemEffectMacOS in `RCTConvert.mm:

This is missing from the Fabric Color conversion code ( https://github.com/microsoft/react-native-macos/blob/721a5aa852add0a8dc0beb09b86c47d369268199/packages/react-native/ReactCommon/react/renderer/graphics/platform/ios/react/renderer/graphics/HostPlatformColor.mm ).