VTK Doxygen Documentation is limited to nightly. It should contains release versions of VTK as well.
One can access VTK Doxygen doc here : https://vtk.org/doc/nightly/html/
However, only nightly is available.
It would be nice if specific release were available, like on ParaView Doxygen doc : https://kitware.github.io/paraview-docs/latest/cxx/