/usr/lib/x86_64-linux-gnu/libmpfi.so is in libmpfi0-dev 1.5.1+ds-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libmpfi.so.0.0.0
/usr/lib/x86_64-linux-gnu/libmpfi.so.0.0.0