/usr/lib/libgalera_smm.so is in percona-xtradb-cluster-server-5.7 5.7.20-29.24-0ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/galera3/libgalera_smm.so
/usr/lib/galera3/libgalera_smm.so