Currently, every time you export Unity using Flutter embed -> Export project to Flutter app (ios) you then need to remember to change the target membership of the Data folder to UnityFramework, and add the linker flags -Wl,-U,_FlutterEmbedUnityIos_sendToFlutter to the Unity-iPhone project build settings.

It would be better if this was automated as part of the export, using Unity's PBXProject editing tool. Looking for anyone with experience with editing Xcode project files to help on this :)