/usr/lib/x86_64-linux-gnu/libboost_mpi_python3.a is in libboost-mpi-python1.65-dev 1.65.1+dfsg-0ubuntu5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libboost_mpi_python3-py36.a