/usr/lib/x86_64-linux-gnu/mod_spatialite.so.7 is in libsqlite3-mod-spatialite 4.3.0a-5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/mod_spatialite.so.7.1.0
/usr/lib/x86_64-linux-gnu/mod_spatialite.so.7.1.0