I did this update today and it bricked my device until i redid it with rsync. I am pretty used to the Anyma phi "dying" and getting bricked when trying to follow the official Ayodyo instructions on MacOS, it has happened every firmware update that i done so far. The rsync solution mentioned in the thread does repair it.
I think it is sad that Ayodyo points to Apple, as if Apple is ever going to change their disk protocol or priorities because some small synth manufacturer in France is bricking devices with it. Ayodyo should just update the README and include the rsync in the instructions, or better, write an installer that reproducible performs the update without bricking the device. Should i risk buying the more expensive Anyma Omega in a few months from now if i am not sure the firmware update will brick the device?
What seems to go wrong is that if you don't use rsync, the 2 updates that happen, (titled "Anyma" and "Synth" ) happen in parallel on the Mac. Whereas if you use rsync they are transfered 1 at the time. That makes me think that it is actually not an Apple bug causing the issue, but rather Aydyo not anticipating the fact that the files will be transfered in parallel like Apple does.
A second difference is that without rsync an eject happens automatically and maybe a bit too early (no way to see visually). when using rsync you can eject manually after both the files have been transfered.