brightness not working on kernel 5.4 and login loop on kernel 5.8 package grub-efi-amd64-signed 1.142.10+2.04-1ubuntu26.8 failed to install/upgrade: installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1

[Luis Martinez]

I have tried many solutions I've found on forums but I just can't fix it.

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: grub-efi-amd64-signed 1.142.10+2.04-1ubuntu26.8
ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.16
Architecture: amd64
CasperMD5CheckResult: skip
Date: Tue Feb 16 22:42:44 2021
ErrorMessage: installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2021-02-16 (1 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
Python3Details: /usr/bin/python3.8, Python 3.8.5, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: N/A
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.4
SourcePackage: grub2-signed
Title: package grub-efi-amd64-signed 1.142.10+2.04-1ubuntu26.8 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)