In case anyone else needs to upgrade NVMe firmware for a WD drive in #FreeBSD or #Linux, here is the WD site with the device list:

https://wddashboarddownloads.wdc.com/wdDashboard/config/devices/lista_devices.xml

So open up your drive model like this:
https://wddashboarddownloads.wdc.com/wdDashboard/firmware/WD_BLACK_SN770_2TB/731130WD/device_properties.xml

And change the "device_properties.xml" in the URL to the ".fluf" file given in the XML, like this:

https://wddashboarddownloads.wdc.com/wdDashboard/firmware/WD_BLACK_SN770_2TB/731130WD/731130WD.fluf

then, for FreeBSD follow the commands given in the manual:
https://man.freebsd.org/cgi/man.cgi?query=nvmecontrol&sektion=8&format=html

ie.

nvmecontrol identify nvme0 | grep -i 'firmware'
nvmecontrol firmware -s 1 -f 731130WD.fluf nvme0
nvmecontrol firmware -s 1 -a nvme0
nvmecontrol reset nvme0