The game doesn't appear to receive mouse input on MacOS. We believe we've identified this as an allegro issue, and a bug report has been filed upstream.
On the 17th of August a possible fix for this was committed to Allegro git (see latest comment in the link above).
I'll see if I can't wrangle someone with access to a Mac and willingness to test :)
Fixed up bug link.
Misc bugfixes courtesy of Trent Gamblin (who also fixed #1 upstream).