I installed to my Apple Silicon Mac via Homebrew and found that the launchd agent was failing due to a nonexistent /usr/local/var/log directory. I created the directory and gave myself write permissions, so it's working for me now. I'm not sure this is the truly correct answer, but I'll assume my own risks there.
I think the correct answer for a Homebrew package would be to point the launchd agent to $HOMEBREW_PREFIX/var/log.
For generic macOS users, would the right target be ~/Library/Logs, which would also work for Homebrew people who are coming via tapping gitjournal/tap?