The bless tool was unable to set the current boot disk.

[dimme]

I have a 2019 iMac with windows 10 on a external SSD via thunderbolt (it's a TB2 enclosure w/ a TB3 to TB2 adapter)> Windows boot and works fine if I hold down the option key at boot up and select the disk. The disk is only identified as efi boot. I can not select the disk in the startup up disk system preference panel. When I do I get the error "The bless tool was unable to set the current boot disk." I used this same setup on ly 2015 iMac for years with no problem. I am running the latest Mojave & Windows 10 OS. Looking for a solution? Thanks

 

[lowendlinux]

Bless doesn't work with APFS and it's being replaced

systemsetup -setstartupdisk /Volume/Thatdisk

is kind of the new bless