Unfortunately, Unity’s Drawers do not work within FlowCanvas (either nodes or variables). That is because Unity drawers are very coupled with it’s own serialization system, whereas FlowCanvas is using a custom serializer. This is why FC also comes with its own custom drawers (both property and object drawers). These work similar to Unity drawers, but it is a different system. This will require re-implementing the drawer, but unfortunately making FC work out of the box with Unity native drawer was far from possible the last time I tried without a plethora of ugly hacks.
