/usr/lib/x86_64-linux-gnu/libass.so is in libass-dev 0.10.0-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libass.so.4.1.0
/usr/lib/x86_64-linux-gnu/libass.so.4.1.0