When you run grub-install by default it assumes the EFI system is mounted as /boot/efi
It depends on your distribution where EFI system is mounted and on some distributions it isn't mounted after boot.
First check if /boot/efi is mounted with
mount | grep /boot/efi If that doesn't work first try the following to see if it is mounted elsewhere.
mount | grep /dev/[efi device] If neither of those work do:
mount /dev/[efi device] /mnt Now run:
grub-install --efi-directory=[efi dir] grub-mkconfig -o /boot/grub/grub.cfg where [efi dir] is either /boot/efi or /mnt and [efi device] is the device with the EFI system partition. If you don't know use the command lsblk -o NAME,PARTTYPE,MOUNTPOINT | grep -i "C12A7328-F81F-11D2-BA4B-00A0C93EC93B"