/usr/lib/x86_64-linux-gnu/libsss_nss_idmap.so is in libsss-nss-idmap-dev 1.15.0-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libsss_nss_idmap.so.0.2.0
/usr/lib/x86_64-linux-gnu/libsss_nss_idmap.so.0.2.0