i5b gerd # grub-install /dev/sda3
Installing for x86_64-efi platform.
grub-install: Fehler: cannot find EFI directory.
i5b gerd # grub-install --boot-directory=/boot/grub /dev/sda
Installing for x86_64-efi platform.
grub-install: Fehler: cannot find EFI directory.
i5b gerd # 

see: Cannot find efi directory: issue with grub-install
( https://unix.stackexchange.com/questions/405472/cannot-find-efi-directory-issue-with-grub-install )
   "I am getting error grub-install: error: cannot find EFI directory"
     >  grub-install /dev/sda
     >  grub-install: error: cannot find EFI directory.


- Answer 1:
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 try

mount | grep /dev/sda6
To see if its amounted elsewhere. If neither do:

mount /dev/sda6 /mnt
Now run:

grub-install --efi-directory=/mnt/efi
grub-mkconfig -o /boot/grub/grub.cfg


- Answer 2:
Grub rescue mode can be treated as

set root=(hd0,gpt6)
set prefix=(hd0,gpt6)/boot/grub
insmod normal
normal

Once you login, enter sudo update-grub && sudo grub-install /dev/sda.