Hi again, Finally I've managed to install a fully working grub on the system. The grub installation process from the installer still fails, with the output attached to the previous message, but I found a way to install a fully functional grub in the system following these steps:
1) When the grub installation fails, I accepted installing grub in an external removable media (this, I think, makes the USB work a grub bootable device, but it's no longer functional as booting installer device. Since I can overwrite it again, it's not a big problem). 2) When booting from this new grub USB device, I only get to the grub prompt. I need to issue the following commands (with the right parameter values): root=(lvm/dev/mapper/root-lvm-device) linux /boot/vmlinuz-image-file root=/dev/mapper/root-lvm-device quiet initrd /boot/initrd-file boot to boot the newly installed system. 3) First thing I did, after booting the system, was: grub-install /dev/nvme0n1 which seemed to work and provided a new UEFI boot entry (which didn't require an external USB device), but still took me only to the grub prompt when booting the system. 4) After some googling and reading, I edited the file /etc/default/grub to include the line: GRUB_DISABLE_OS_PROBER=false and executed: update-grub2 on the booted system. This finally provided a fully functional grub installation (it may be that adding the line in /etc/default/grub is not necessary, I didn't check if it worked without that). Finally, I commented out the added line in /etc/default/grub. I think that, in this particular case and for some reason, grub installation doesn't work when done from the installer (maybe I did something wrong?), but works if done from the newly installed system. Of course, you need to find a way to boot that system first. Hope this information helps with the problem! Josep Guerrero