/usr/lib/x86_64-linux-gnu/libpolkit-backend-1.so is in libpolkit-backend-1-dev 0.105-14.1ubuntu0.4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libpolkit-backend-1.so.0.0.0