Hello, Luis
_ZN26vtkImageConnectivityFilter3NewEv is a mangled symbol of vtkImageConnectivityFilter::New(). The class’ header’s documentation (https://vtk.org/doc/nightly/html/vtkImageConnectivityFilter_8h_source.html) tells its path in source directory is Imaging/Morphological. So, I guess its implementation class module library is vtkImagingMorphological-<VTK version>.so/dll. Hence you can try:
VTK_MODULE_INIT(vtkImagingMorphological);
Abstract classes implementation modules are loaded at runtime, much like plug-ins (more about this here: https://vtk.org/Wiki/VTK/Build_System_Migration#How_Implementation_Modules_Are_Initialized). This means that they are not linked to your program at build time, that is, they won’t show up in ldd (Unix) or Dependency Walker (Windows).
I hope this helps.
regards,
Paulo