Comment 5 for bug 1790994

Some more information when trying to fix this.

sudo dpkg --configure -a
Setting up grub-efi-amd64-signed (1.93.5+2.02-2ubuntu8.4) ...
Installing for x86_64-efi platform.
Could not prepare Boot variable: No space left on device
grub-install: error: efibootmgr failed to register the boot entry: Input/output error.
dpkg: error processing package grub-efi-amd64-signed (--configure):
 installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1
dpkg: dependency problems prevent configuration of shim-signed:
 shim-signed depends on grub-efi-amd64-signed; however:
  Package grub-efi-amd64-signed is not configured yet.

dpkg: error processing package shim-signed (--configure):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 grub-efi-amd64-signed
 shim-signed

But /boot has space.
df -h | grep boot
/dev/sda1 511M 4.7M 507M 1% /boot/efi

Looking at similar problems (https://bugs.launchpad.net/ubuntu/+source/shim-signed/+bug/1776271) could need a BIOS update. Currently

sudo lshw | less
  *-core
       description: Motherboard
       product: 2B47
       vendor: HP
       physical id: 0
       version: 1.04
     *-firmware
          description: BIOS
          vendor: AMI
          physical id: 0
          version: A0.13
          date: 12/21/2015
          size: 64KiB
          capacity: 8128KiB

Have not yet rebooted after the upgrade, but in case reboot fails, I will report back on a different computer.