１，Reinstall the grub-efi package

apt-get install --reinstall grub-efi

先の。

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２，Put the debian bootloader in /boot/efi and create an appropriate entry in the computer NVRAM

grub-install

n@RY:~$ sudo grub-install
Installing for x86_64-efi platform.
Installation finished. No error reported.
n@RY:~$

３，Re create a grub config file based on your disk partitioning schema

update-grub

n@RY:~$ sudo update-grub
Generating grub configuration file ...
Found background image: /usr/share/images/desktop-base/desktop-grub.png
Found linux image: /boot/vmlinuz-5.10.0-7-amd64
Found initrd image: /boot/initrd.img-5.10.0-7-amd64
Adding boot menu entry for EFI firmware configuration
done
n@RY:~$

４，You should check afterwards that:
その後、次のことを確認する必要があります。

Check 1. the bootloader is existing in /boot/efi/EFI/debian/grubx64.efi
チェック1.ブートローダーが/boot/efi/EFI/debian/grubx64.efiに存在する

$ file /boot/efi/EFI/debian/grubx64.efi

/boot/efi/EFI/debian/grubx64.efi: PE32+ executable (EFI application) x86-64 (stripped to external PDB), for MS Windows

チェック！

Check 2. the nvram entry was properly created.
チェック2.nvramエントリが正しく作成されました。

$ efibootmgr --verbose | grep debian
Boot0000* debian HD(1,MBR,0x8cbb0b4f,0x800,0x40000)/File(\EFI\debian\shimx64.efi)

$ You can now reboot, and Grub should greet you.
これで再起動でき、Grubがあなたに挨拶するはずです。