Somehow the SecureBoot keys that are installed by default on my laptop were deleted. Once I "Factory Restored" those SecureBoot keys in my UEFI System Settings, then the Ubuntu installer would finish installing without error.
So the only thing that would have really helped would have been a helpful error message when the grub2-efi-signed package failed to install.
I finally discovered what the problem was:
Somehow the SecureBoot keys that are installed by default on my laptop were deleted. Once I "Factory Restored" those SecureBoot keys in my UEFI System Settings, then the Ubuntu installer would finish installing without error.
So the only thing that would have really helped would have been a helpful error message when the grub2-efi-signed package failed to install.