Comment 6 for bug 1761336

I had a look at the set of modules being loaded by the grub.cfg. The only line that seems like it wouldn't be satisfied is:

        if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi

There is no lzopio module being included in grubx64.efi.

However, I have this in my own grub.cfg as well, and it doesn't cause any failure to boot.

Otherwise, the config looks uneventful. your boot entries do show that you have the .signed kernel installed, so it should be bootable.

If you try to individually run the commands listed in /boot/efi/EFI/ubuntu/grub.cfg at the grub prompt, what happens?:

search.fs_uuid 908780ee-820c-44ee-9625-2bd693097849 root hd1,gpt4
set prefix=($root)'/boot/grub'
configfile $prefix/grub.cfg