Reinstall grub
Startup system with Debian Live USB key.
Prepare envirnoment to chroot
Mount system (here with boot included)
mount /dev/nvme1n1p2 /mnt # with /boot included in root
mount -t sysfs /sys /mnt/sys
mount -t proc /proc /mnt/proc
mount -o bind /dev /mnt/dev
Mount efi requirements
mount /dev/nvme1n1p1 /mnt/boot/efi # efi
mount -t efivarfs none /mnt/sys/firmware/efi/efivars
When environment is ready
chroot /mnt
grub-install
update-grub
Check the NVRAM
efibootmgr --verbose | grep debian
Correct result (HD after debian is important)
Boot0001* debian HD(1,GPT,b57757cd-9568-4135-a033-c7e6af81947d,0x800,0x100000)/File(\EFI\debian\shimx64.efi)