/usr/lib/x86_64-linux-gnu/libidn2.so.0 is in libidn2-0 0.16-1+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libidn2.so.0.1.4
/usr/lib/x86_64-linux-gnu/libidn2.so.0.1.4