package grub-efi-amd64-signed 1.93.13+2.02-2ubuntu8.12 failed to install/upgrade: installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1

your system has UEFI Secure Boot enabled firmware, and the following kernels present on your system are unassigned:

4.19.0-041900 Generic

These kernels cannot be verified Under Secure Boot.

ProblemType: Package
DistroRelease: Ubuntu 18.04
Package: grub-efi-amd64-signed 1.93.13+2.02-2ubuntu8.12
Uname: Linux 4.19.0-041900-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.6
Architecture: amd64
Date: Sat Mar 16 11:10:01 2019
ErrorMessage: installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2018-10-26 (141 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
Python3Details: /usr/bin/python3.6, Python 3.6.7, python3-minimal, 3.6.7-1~18.04
PythonDetails: N/A
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu2.1
 apt 1.6.8
SourcePackage: grub2-signed
Title: package grub-efi-amd64-signed 1.93.13+2.02-2ubuntu8.12 failed to install/upgrade: installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)