I know this might seem stupid as I don't own a Mac, but does Darwin use systemd? Can the author use journalctl, syslog or check /var/log?
Darwin uses launchd/libxpc. journalctl's job is handled by the `log` command, with appropriate predicate filters to winnow out the relevant stuff from the chaff.
> does Darwin use systemd?
No.
It has the thing that systemd and journalctl are poor clones of.
Their ergonomics (especially the log viewer) are much worse than sysvinit/syslog, but they mostly work.
I say “mostly”, because, like systemd, sometimes force disabling a broken service silently fails, even after reboot.