With focal image released 2020-09-07 while retrofitting an image an update to the grub-efi-amd64-signed package will be attempted, but it fails:
Setting up grub-efi-amd64-signed (1.142.6+2.04-1ubuntu26.4) ...
Trying to migrate /boot/efi into esp config
dpkg: error processing package grub-efi-amd64-signed (--configure):
installed grub-efi-amd64-signed package post-installation script
subprocess returned error exit status 1
Running the post-install with debugging reveals this:
+ /usr/lib/grub/grub-multi-install --target=x86_64-efi
debconf: unable to initialize frontend: Dialog
debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell buffer, or without a controlling terminal.)
debconf: falling back to frontend: Readline
debconf: unable to initialize frontend: Readline
debconf: (This frontend requires a controlling tty.)
debconf: falling back to frontend: Teletype
Trying to migrate /boot/efi into esp config
You chose not to install GRUB to any devices. If you continue, the boot loader
may not be properly configured, and when this computer next starts up it will
use whatever was previously configured. If there is an earlier version of GRUB 2
in the EFI system partition, it may be unable to load modules or handle the
current configuration file.
If you are already using a different boot loader and want to carry on doing so,
or if this is a special environment where you do not need a boot loader, then
you should continue anyway. Otherwise, you should install GRUB somewhere.
Continue without installing GRUB? [yes/no]
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