#1, on your HAP-Z1ES unit, press the Power and Home buttons simultaneously.
#2, select change SMB address, dial to select SMB version 1.0.
#3, scroll down and select Restart.
#4, power unit on and then start the HAP Music Transfer app on your Mac computer.
#5, be aware that file transfers will now take longer.
#6, watch the Sony HAP-Z1ES support page for an update in the next few weeks.
Do note:The transfer was a bit slower but not much slower than usual - 5+ minutes for ~700mb
*The unit should be off when you first start the steps outlined in JDAWG's post. And you should release the Power & Home button when you see the SONY come up. If you hold it too long it'll just power up and power down.
*The workaround seems to continue working after you power down, so, at least in my case, I didn't need to repeat these steps each time I wanted to transfer after turning the unit on.
(With large thanks to Shawn of Sony ES, and the various discussants in the Sony Community HAP-Z1ES thread, notably JDAWG and User1623339705956324586.