I had the same linking error while building VTK today. (Visual Studio Professional 2022 (64-bit) - Version 17.6.2)
181>vtkCommonCore-9.3d.lib(vtkCommonCore-9.3d.dll) : error LNK2005: "public: __cdecl vtkConstantImplicitBackend<float>::vtkConstantImplicitBackend<float>(float)" (??0?$vtkConstantImplicitBackend@M@@QEAA@M@Z) already defined in vtkToImplicitRamerDouglasPeuckerStrategy.obj
181>vtkCommonCore-9.3d.lib(vtkCommonCore-9.3d.dll) : error LNK2005: "public: __cdecl vtkConstantImplicitBackend<double>::vtkConstantImplicitBackend<double>(double)" (??0?$vtkConstantImplicitBackend@N@@QEAA@N@Z) already defined in vtkToImplicitRamerDouglasPeuckerStrategy.obj
etc ...
...
I could build the library after editing the header file vtkCompositeImplicitBackend.h removing the export from the vtkConstantImplicitBackend struct.
thanks to vividege (fix described above).
C.