While making an upgrade (Ubuntu 20.04 to Ubuntu 21.04) I faced this issue with error code: -65537.

[skouros]

Error message: Installed postfixed package post-installation script subprocess return error exit status 75.
error code: -65537

Description: Ubuntu 21.04
Release: 21.04

linux-image-extra-virtual-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-tools-generic-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-cloud-tools-generic-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-image-generic-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-tools-lowlatency-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-cloud-tools-lowlatency-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-headers-virtual-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-virtual-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-image-extra-virtual-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-oem-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-virtual-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-lowlatency-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-tools-virtual-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-cloud-tools-virtual-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-headers-generic-hwe-20.04:
  Installed: 5.11.0.25.27
  Candidate: 5.11.0.25.27
  Version table:
 *** 5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
        100 /var/lib/dpkg/status
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-generic-hwe-20.04:
  Installed: 5.11.0.25.27
  Candidate: 5.11.0.25.27
  Version table:
 *** 5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
        100 /var/lib/dpkg/status
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-image-lowlatency-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-cloud-tools-generic-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-tools-lowlatency-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-headers-generic-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-headers-lowlatency-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-cloud-tools-virtual-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-image-oem-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-image-virtual-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-tools-oem-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-headers-oem-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-image-lowlatency-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-lowlatency-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-generic-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-tools-generic-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-image-virtual-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-headers-lowlatency-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-cloud-tools-lowlatency-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-tools-virtual-hwe-20.04:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-headers-virtual-hwe-20.04-edge:
  Installed: (none)
  Candidate: 5.11.0.25.27
  Version table:
     5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages
linux-image-generic-hwe-20.04:
  Installed: 5.11.0.25.27
  Candidate: 5.11.0.25.27
  Version table:
 *** 5.11.0.25.27 500
        500 http://archive.ubuntu.com/ubuntu hirsute-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu hirsute-security/main amd64 Packages
        100 /var/lib/dpkg/status
     5.11.0.16.17 500
        500 http://archive.ubuntu.com/ubuntu hirsute/main amd64 Packages

Expected Behavior:
As a user I expected to make the upgrade successfully.

Actual Behavior:
After this issue, the upgrade program continue to installing the upgrades but after a minute another error occured:

"Could not install the upgrades

The upgrade has aborted. Your system could be in an unusable state. A recovery will run now (dpkg --configure -a)."

Regardless this message the upgrade program continue and final I got this message:
"Upgrade complete

The upgrade has completed but there were errors during the upgrade process."

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: ubuntu-release-upgrader-core 1:21.04.14
ProcVersionSignature: Ubuntu 5.8.0-63.71~20.04.1-generic 5.8.18
Uname: Linux 5.8.0-63-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu65.1
Architecture: amd64
CasperMD5CheckResult: unknown
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Tue Jul 27 15:47:16 2021
InstallationDate: Installed on 2021-04-07 (110 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: ubuntu-release-upgrader
UpgradeStatus: Upgraded to hirsute on 2021-07-27 (0 days ago)
VarLogDistupgradeTermlog: