Hi, so I went on using the same files than you, and was able to install the linux kernel and grub. I added a few more information below, so please try again and check that the output matches (especially the one about the EFI variables).
1/ Expand the size of the virtual disk. Default size is not big enough to install the additional linux kernel. This can be done from the web interface. I used 8 GB.
2/ First edit /etc/fstab to put the first partition into /boot/efi. Debian needs an ext4 partition for /boot.. Also add efivarfs to solve the "EFI Variables are not supported on this system" issue:
proc /proc proc defaults 0 0
PARTUUID=50a67c3e-01 /boot/efi vfat defaults,flush 0 2
PARTUUID=50a67c3e-02 / ext4 defaults,noatime 0 1
none /sys/firmware/efi/efivars efivarfs defaults
3/ umount /boot && mkdir /boot/efi && mount /boot/efi && mount /sys/firmware/efi/efivars
You should now be able to see the EFI variables:
root@debian:~# ls /sys/firmware/efi/efivars/
Boot0000-8be4df61-93ca-11d2-aa0d-00e098032b8c
Boot0001-8be4df61-93ca-11d2-aa0d-00e098032b8c
Boot0002-8be4df61-93ca-11d2-aa0d-00e098032b8c
Boot0003-8be4df61-93ca-11d2-aa0d-00e098032b8c
Boot0004-8be4df61-93ca-11d2-aa0d-00e098032b8c
Boot0005-8be4df61-93ca-11d2-aa0d-00e098032b8c
BootCurrent-8be4df61-93ca-11d2-aa0d-00e098032b8c
BootOptionSupport-8be4df61-93ca-11d2-aa0d-00e098032b8c
BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c
ConIn-8be4df61-93ca-11d2-aa0d-00e098032b8c
ConInDev-8be4df61-93ca-11d2-aa0d-00e098032b8c
ConOut-8be4df61-93ca-11d2-aa0d-00e098032b8c
ConOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c
db-d719b2cb-3d3a-4596-a3bc-dad00e67656f
dbx-d719b2cb-3d3a-4596-a3bc-dad00e67656f
ErrOut-8be4df61-93ca-11d2-aa0d-00e098032b8c
ErrOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c
KEK-8be4df61-93ca-11d2-aa0d-00e098032b8c
Lang-8be4df61-93ca-11d2-aa0d-00e098032b8c
LangCodes-8be4df61-93ca-11d2-aa0d-00e098032b8c
OsIndicationsSupported-8be4df61-93ca-11d2-aa0d-00e098032b8c
PerfDataMemAddr-76b6bdfa-2acd-4462-9e3f-cb58c969d937
PK-8be4df61-93ca-11d2-aa0d-00e098032b8c
PL031RtcDaylight-b336f62d-4135-4a55-ae4e-4971bbf0885d
PL031RtcTimeZone-b336f62d-4135-4a55-ae4e-4971bbf0885d
PlatformLang-8be4df61-93ca-11d2-aa0d-00e098032b8c
PlatformLangCodes-8be4df61-93ca-11d2-aa0d-00e098032b8c
SbConfigState-793d9786-44dc-4709-b57f-85b8e8fdbfd2
Timeout-8be4df61-93ca-11d2-aa0d-00e098032b8c
4/ Increase root partition size: raspi-config --expand-rootfs ; resize2fs /dev/sda2
5/ install the kernel: apt update && apt install linux-image-arm64 grub-efi-arm64
6/ install grub: grub-install ; update-grub2
root@debian:~# grub-install
Installing for arm64-efi platform.
Installation finished. No error reported.
root@debian:~# update-grub2
Generating grub configuration file ...
Found background image: /usr/share/images/desktop-base/desktop-grub.png
Found linux image: /boot/vmlinuz-5.10.0-14-arm64
Found initrd image: /boot/initrd.img-5.10.0-14-arm64
Adding boot menu entry for EFI firmware configuration
done
7/ exit, eject the cdrom and reboot

