/usr/lib/x86_64-linux-gnu/lua/5.3/mpack.so is in lua-mpack 1.0.7-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/lua/5.3/../../liblua5.3-mpack.so.0.0.0
/usr/lib/x86_64-linux-gnu/lua/5.3/../../liblua5.3-mpack.so.0.0.0