/usr/lib/x86_64-linux-gnu/libsfml-system.so is in libsfml-dev 2.4.2+dfsg-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libsfml-system.so.2.4
/usr/lib/x86_64-linux-gnu/libsfml-system.so.2.4