/usr/lib/x86_64-linux-gnu/libpolyml.so is in libpolyml-dev 5.7.1-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libpolyml.so.9.0.0
/usr/lib/x86_64-linux-gnu/libpolyml.so.9.0.0