I don’t know where to put this and I am sure others have had this issue.
After Windows did an update I was left at this prompt:
ERROR: Unknown filesystem
Entering Rescue Mode . . .
Grub Rescue>_
Not to panic at this point.
I entered this command and rebooted and all was well:
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=manjaro --recheck