Hi Sankesh,
Thanks a lot for your reply. The solution you describe does exactly what I already tried (as I wrote in my question). My CMAKE_PREFIX_PATH is printed in the cmake output I added to the post and clearly shows that the path ‘E:/Qt/6.8.0/msvc2022_64/lib/cmake/Qt6QmlTools’ has been successfully added. As I described, I also verified that the module paths contains the expected *Config.cmake files. Strangely, it only fails with Qt6QmlTools, the rest of the module paths are correctly found.
For now, I have been able to configure and compile VTK by adding ‘-DQt6QmlTools_DIR:PATH=${QT_EXT_BUILD}/lib/cmake/Qt6QmlTools’ to VTK’s ExternalProject_Add CMAKE_ARGS. But to me this still feels a bit like an ugly hack.
I also changed '-DVTK_GROUP_ENABLE_Qt:STRING=‘YES’ from ‘-DVTK_GROUP_ENABLE_QT:STRING=‘YES’’ (note the _Qt instead of _QT)
Maybe this helps fellow VTK fans struggling with their builds.