You could probably export (XPostProcessor.VtkExporter or XPostProcessor.VtkXmlExporter, not sure it is in s4l_v1) it as a VTK file and modify your neural network DataLoader to support VTK files, e.g., via the meshio package or the much larger vtk package, or many others.
Or you could write a little Python script to grab the field data and save it to npy. To access the field, you would get the output of the extractor or pipeline entity in the analysis, say a FloatFieldData object. It has a Field(self, index: int) -> np.ndarray method to get the field as a numpy array, which you could save using e.g., np.save("filename.npy", fd.Field(0))