/usr/lib/libITKFFT-4.12.so is in libinsighttoolkit4-dev 4.12.2-dfsg1-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libITKFFT-4.12.so.1
/usr/lib/libITKFFT-4.12.so.1