Well, I retried installing and was asked my password which seemed to install it. Then tried the first conversion which seemed to work ie I saw the same output that the Windows version gives when I drop files on it. See:
Last login: Tue Sep 29 21:29:36 on ttys000
steveparry@MacBook-Pro ~ % kepubify/Users/steveparry/Desktop/Kepubifiying/Awaiting\ Conversion/A\ Natural\ History\ of\ Love\ \(2011\)\ -\ Diane\ Ackerman.epub
zsh: no such file or directory: kepubify/Users/steveparry/Desktop/Kepubifiying/Awaiting Conversion/A Natural History of Love (2011) - Diane Ackerman.epub
steveparry@MacBook-Pro ~ % kepubify</Users/steveparry/Desktop/Kepubifiying/Awaiting\ Conversion/A\ Natural\ History\ of\ Love\ \(2011\)\ -\ Diane\ Ackerman.epub >
zsh: parse error near `\n'
steveparry@MacBook-Pro ~ % kepubify /Users/steveparry/Desktop/Kepubifiying/Awaiting\ Conversion/A\ Natural\ History\ of\ Love\ \(2011\)\ -\ Diane\ Ackerman.epub
Kepubify v3.1.4
[ 1/ 1] Converting /Users/steveparry/Desktop/Kepubifiying/Awaiting Conversion/A Natural History of Love (2011) - Diane Ackerman.epub
1 total: 1 converted, 0 copied, 0 skipped, 0 errored
steveparry@MacBook-Pro ~ %
But I can't find the converted file! Edit: I found the files! Kepubify is converting them and putting them back onto the /users/ folder. See attached screenshot:
https://photos.app.goo.gl/xTdsi6PG2XiZaWgv8