I solved this problem by creating a 64GB volume and manually installing Windows 10 on it. I did not use BootCamp, just a bootable USB with Windows 10. The resulting Windows is very slow (be patient - no drivers) but I was able to install WD software to check for the WD550 firmware.Here I am again, postscript: WD does not have a Firmware Check/Update Tool for Mac! This is truly intolerable!
So:
- I don't know what firmware my disk has
- I won't be able to update it anyway
(unless I take everything apart, connect it to a Windows PC with a USB adapter, etc etc...😡)