It looks like a compile problem. Check the .pro file that it contains the correct statement of .lib(or .a) files, like the this:
LIBS += C:\VTK\VTK-9.0.1_mingw_debug\lib\lib*.*
And the path of VTK(like “C:\VTK\VTK-9.0.1_mingw_debug\bin”) contains .dll files should be added to the building environment in Qt Creator or path environment of your system, or you can copy the .dll files to the directory of your App.