/usr/lib/x86_64-linux-gnu/libproj.so is in libproj-dev 4.9.3-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libproj.so.12.0.0
/usr/lib/x86_64-linux-gnu/libproj.so.12.0.0