/usr/lib/x86_64-linux-gnu/libnfsidmap.so is in libnfsidmap-dev 0.25-5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /lib/x86_64-linux-gnu/libnfsidmap.so.0.3.0
/lib/x86_64-linux-gnu/libnfsidmap.so.0.3.0