/usr/lib/x86_64-linux-gnu/libnotify.so.4 is in libnotify4 0.7.6-2svn1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libnotify.so.4.0.0
/usr/lib/x86_64-linux-gnu/libnotify.so.4.0.0