DiagonalArg, the entire grub.cfg is as follows:
search.fs_uuid <your efi fs uuid> efs insmod ($efs)/EFI/ubuntu/f2fs.mod search.fs_uuid <your f2fs fs uuid> root set prefix=($root)'/boot/grub' configfile $prefix/grub.cfg
DiagonalArg, the entire grub.cfg is as follows:
search.fs_uuid <your efi fs uuid> efs EFI/ubuntu/ f2fs.mod ($root) '/boot/ grub'
insmod ($efs)/
search.fs_uuid <your f2fs fs uuid> root
set prefix=
configfile $prefix/grub.cfg