/usr/lib/x86_64-linux-gnu/libnautilus-extension.so is in libnautilus-extension-dev 3.22.3-1+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libnautilus-extension.so.1.4.0