Incidently the std::cout errors reported here are triggered by vtk 9.6. Previously vtk had been including the headers and declaring use of std::cout etc. It stoppe doing that in MR#11993 https://gitlab.kitware.com/vtk/vtk/-/merge_requests/11993
So this bug had been present earlier, but was hidden by previous versions of vtk. Files which are using std:: objects must #include their respective headers.
