/usr/lib/x86_64-linux-gnu/libpolyml.so is in libpolyml-dev 5.6-8.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libpolyml.so.7.0.0
/usr/lib/x86_64-linux-gnu/libpolyml.so.7.0.0