/usr/share/man/fr/man2/mpx.2.gz is in manpages-fr-dev 3.65d1p1-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/fr/man2/unimplemented.2.gz
/usr/share/man/fr/man2/unimplemented.2.gz