Grub installation failed

Fixed the efibootmgr errors by mounting the Boot variables for efibootmgr :

# mount -t efivarfs efivarfs /sys/firmware/efi/efivars

And then efibootmgr gave me errors about space :

Could not prepare Boot variable: No space left on device

Fixed that by deleting dump files :

# rm /sys/firmware/efi/efivars/dump-*

And then ran the usual

update-grub 
grub-install -v --target=x86_64-efi --recheck /dev/sda

and it ran successfully!

Try to specify the disk containing the loader if your disk is not /dev/sda:

efibootmgr --create --disk /dev/nvme0n1 --part 1 --label Ubuntu