Hmm, now I have no idea.
I see a message that VTK_USE_FILE is no longer used since 8.90,
but,
the current vtk.git/Examples/Tutorial/Step1/Cxx/CMakeLists.txt
still has VTK_USE_FILE …
I found the new method here:
3645 topic
Would be great if it were documented and examples updated etc, or at least drop a readme in there that is blindingly obvious to find. There might already be something in there, but I might be more blind than most…