Thank you for reporting this issue to us. We have confirmed that there is a bug in macOS 10.15.1 that prevents macOS from using the USB bootloader that we provide on the A-Star 32U4, Zumo 32U4, Balboa 32U4, and Romi 32U4 boards. We have made a new version of the bootloader that works around the bug. You can download it here:
a-star-32u4-bootloader-191104.zip (63.2 KB)
If you use an AVR programmer to flash the HEX file onto your board, you should then be able to program it from your Mac. However, please note that this is an experimental new build of the bootloader that we have not fully tested yet. If you try it out, please tell us whether it works for you. Thanks again!