f is definitely a switch:
/f Used with the /s command, specifies the firmware type of the
target system partition. Options for <firmware> are 'UEFI',
'BIOS', or 'ALL'.
I dunno, try this:
bcdboot X:\Windows /f ALL /s D:
X is where your current boot files are at. It could be on the hidden system partition. In that case, you'll need a workaround.
The following example copies BCD files that support booting on either a UEFI-based or a BIOS-based computer from the C:\Windows folder to a system partition that was assigned the volume letter S:
BCDboot Command-Line Options
bcdboot C:\Windows /f ALL /s S:
Try this if still needed:
bcdboot C: /f ALL /s D: