/usr/lib/x86_64-linux-gnu/libmuffin.so is in libmuffin-dev 2.2.6-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libmuffin.so.0.0.0
/usr/lib/x86_64-linux-gnu/libmuffin.so.0.0.0