/usr/lib/x86_64-linux-gnu/libprotobuf-c.so is in libprotobuf-c-dev 1.2.1-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libprotobuf-c.so.1.0.0
/usr/lib/x86_64-linux-gnu/libprotobuf-c.so.1.0.0