/usr/lib/x86_64-linux-gnu/libspatialite.so is in libspatialite-dev 4.3.0a-5build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libspatialite.so.7.1.0
/usr/lib/x86_64-linux-gnu/libspatialite.so.7.1.0