/usr/lib/x86_64-linux-gnu/libnettle.so.4 is in libnettle4 2.4-1ubuntu0.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libnettle.so.4.3
/usr/lib/x86_64-linux-gnu/libnettle.so.4.3