package shim-signed 1.40.3+15+1533136590.3beb971-0ubuntu1 failed to install/upgrade: installed shim-signed package post-installation script subprocess returned error exit status 1

I do not know. Just a fresh install on this completely clean machine. After the very first boot, just clicking through the Welcome to Ubuntu dialog and this bug comes up. And btw, the only way to install Ubuntu on this machine was in "save graphics" mode. Otherwise, it freezes completely during setup. What a surprise. Nvidia has never worked properly on Linux! :(

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: shim-signed 1.40.3+15+1533136590.3beb971-0ubuntu1
ProcVersionSignature: Ubuntu 5.4.0-26.30-generic 5.4.30
Uname: Linux 5.4.0-26-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
.proc.sys.kernel.moksbstate_disabled: Error: [Errno 2] No such file or directory: '/proc/sys/kernel/moksbstate_disabled'
ApportVersion: 2.20.11-0ubuntu27
AptOrdering:
 shim:amd64: Install
 shim-signed:amd64: Install
 NULL: ConfigurePending
Architecture: amd64
BootEFIContents:
 BOOTX64.CSV
 grub.cfg
 grubx64.efi
 mmx64.efi
 shimx64.efi
CasperMD5CheckResult: skip
Date: Thu Apr 23 22:00:52 2020
EFITables:
 apr 23 22:10:12 mato kernel: efi: EFI v2.31 by American Megatrends
 apr 23 22:10:12 mato kernel: efi: ACPI=0xba5f0000 ACPI 2.0=0xba5f0000 ESRT=0xbced7998 SMBIOS=0xf0570 MPS=0xfd650
 apr 23 22:10:12 mato kernel: secureboot: Secure boot enabled
 apr 23 22:10:12 mato kernel: esrt: Reserving ESRT space from 0x00000000bced7998 to 0x00000000bced79d0.
 apr 23 22:10:12 mato kernel: secureboot: Secure boot enabled
ErrorMessage: installed shim-signed package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2020-04-23 (0 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
Python3Details: /usr/bin/python3.8, Python 3.8.2, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: N/A
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.2
SecureBoot: 6 0 0 0 1
SourcePackage: shim-signed
Title: package shim-signed 1.40.3+15+1533136590.3beb971-0ubuntu1 failed to install/upgrade: installed shim-signed package post-installation script subprocess returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)
---
ProblemType: Bug
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
DistroRelease: Ubuntu 20.04
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash nomodeset ---
InstallationDate: Installed on 2020-04-23 (0 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
NonfreeKernelModules: nvidia_modeset nvidia wl
Package: ubiquity (not installed)
ProcVersionSignature: Ubuntu 5.4.0-26.30-generic 5.4.30
Tags: focal ubiquity-20.04.15
Uname: Linux 5.4.0-26-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin lxd plugdev sambashare sudo
_MarkForUpload: True