/usr/share/man/man8/systemd-journal-gatewayd.8.gz is in systemd-journal-remote 229-4ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man8/systemd-journal-gatewayd.service.8.gz
/usr/share/man/man8/systemd-journal-gatewayd.service.8.gz