Hello !
I tried to upgrade Calibre that was installed on my MacBook Pro (Mojave) with the last downloaded version on the main site (Disk iMaGe file).
The installation fails with a message "No Mountable File Systems" at the end of the checkup of the archive. I get the same error on the previous available version 5.4.2.
It works with 5.4.1.
I hope you could correct it for the next version
Regards,
Diego