Dual boot (separate drive)

Hi there,

I'm getting

EFI variables are not supported on this system.
Cannot find Windows boot in EFI, exiting

EFI variables are not supported on this system.
Cannot find Windows boot in EFI, exiting

when trying to use

boot-windows

boot-windows

.

My Windows boot is visible in my bios menu, for reference, but it's not visible in grub.