Installation semi dies at end

[JXT]

installed shim-signed package post-installation script subprocess returned error exit status 1

I've had this on Xubuntu 20.04 and Kubuntu 21.04. Installation get to the end, errors with the above and the installer kinda crashes rather than allowing input. System isn't bootable after with Grub failed boot detection the dmesg as it's trying to boot before hanging on a black screen.

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: ubuntu-release-upgrader-core 1:21.04.10
ProcVersionSignature: Ubuntu 5.11.0-16.17-generic 5.11.12
Uname: Linux 5.11.0-16-generic x86_64
ApportVersion: 2.20.11-0ubuntu65
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.461
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Fri Sep 3 00:13:01 2021
LiveMediaBuild: Kubuntu 21.04 "Hirsute Hippo" - Release amd64 (20210420)
PackageArchitecture: all
RebootRequiredPkgs:
 linux-image-5.11.0-16-generic
 linux-image-5.11.0-31-generic
SourcePackage: ubuntu-release-upgrader
Symptom: dist-upgrade
UpgradeStatus: No upgrade log present (probably fresh install)