/usr/lib/x86_64-linux-gnu/libmpg123.so.0 is in libmpg123-0 1.12.1-3.2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libmpg123.so.0.25.1
/usr/lib/x86_64-linux-gnu/libmpg123.so.0.25.1