/usr/lib/ldap/back_ldap-2.4.so.2 is in slapd 2.4.28-1.1ubuntu4.6.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ldap/back_ldap-2.4.so.2.8.1
/usr/lib/ldap/back_ldap-2.4.so.2.8.1