@Sabbrad6, thank you very much. I was able to boot once again into umbrel and restore the data. However, I’m still facing an issue to properly booting the system, since manually installing grub doesn’t seem to work. I have more details here X86 system do not find boot device after installation (solved) - #10 by brnbc
At least, I can manually use super grub 2 disk to manually boot the system.
Thank you for your time!