I followed your advice and tried to bootstrap directly Debian into the eMMC
module, but at the end of the process GRUB is still not found, clearly I am missing some key steps but do not which ones.
CHROOT:
create and update grub
echo "GRUB_ENABLE_CRYPTODISK=y" >> /etc/default/grub
grub-install /dev/mmcblk0
[OK]
update-grub
[OK]
Exit CHROOT
Reflash bootloader
cd libre[tab]
./lfth.sh bl-flash roc-rk3328-cc mmcblk0 verify
[OK]
Reboot (removing the SD Card)
Did not work 
Unfortunately after the reboot it does’t boot.
If I connect the board through HDMI → VGA I can display the buffer, on this other monitor HDMI → HDMI I can’t but the green light is not blinking.
I don’t know where I am mistaken, perhaps this can help anyone to spot it out. I can provide some logs just tell me which I should grab from the eMMC
, thanks!